clarify use of term 'context'

The term 'context' is vague and overloaded. Its usage for 'an execution
context' is now referred as such, in both comments and some APIs' names.
When the execution context can only be a fiber or a task (i.e. not an
ISR), it is referred to as a 'thread', again in comments and everywhere
in the code.

APIs that had their names changed:

  - nano_context_id_t is now nano_thread_id_t
  - context_self_get() is now sys_thread_self_get()
  - context_type_get() is now sys_execution_context_type_get()
  - context_custom_data_set/get() are now
    sys_thread_custom_data_set/get()

The 'context' prefix namespace does not have to be reserved by the
kernel anymore.

The Context Control Structure (CCS) data structure is now the Thread
Control Structure (TCS):

  - struct ccs is now struct tcs
  - tCCS is now tTCS

Change-Id: I7526a76c5b01e7c86333078e2d2e77c9feef5364
Signed-off-by: Benjamin Walsh <benjamin.walsh@windriver.com>

arch/arm/core/swap.S

@@ -55,18 +55,17 @@ GDATA(_nanokernel)
  *
  * @brief PendSV exception handler, handling context switches
  *
- * The PendSV exception is the only context in the system that can perform
- * context switching. When an execution context finds out it has to switch
- * contexts, it pends the PendSV exception.
+ * The PendSV exception is the only execution context in the system that can
+ * perform context switching. When an execution context finds out it has to
+ * switch contexts, it pends the PendSV exception.
  *
  * When PendSV is pended, the decision that a context switch must happen has
  * already been taken. In other words, when __pendsv() runs, we *know* we have
  * to swap *something*.
  *
- * The scheduling algorithm is simple: schedule the head of the runnable FIBER
- * context list, which is represented by _nanokernel.fiber. If there are no
- * runnable FIBER contexts, then schedule the TASK context represented by
- * _nanokernel.task. The _nanokernel.task field will never be NULL.
+ * The scheduling algorithm is simple: schedule the head of the runnable fibers
+ * list (_nanokernel.fiber). If there are no runnable fibers, then schedule the
+ * task (_nanokernel.task). The _nanokernel.task field will never be NULL.
  */
 
 SECTION_FUNC(TEXT, __pendsv)
@@ -80,14 +79,14 @@ SECTION_FUNC(TEXT, __pendsv)
 	pop {lr}
 #endif
 
-    /* load _Nanokernel into r1 and current tCCS into r2 */
+    /* load _Nanokernel into r1 and current tTCS into r2 */
     ldr r1, =_nanokernel
     ldr r2, [r1, #__tNANO_current_OFFSET]
 
-    /* addr of callee-saved regs in CCS in r0 */
-    add r0, r2, #__tCCS_preempReg_OFFSET
+    /* addr of callee-saved regs in TCS in r0 */
+    add r0, r2, #__tTCS_preempReg_OFFSET
 
-    /* save callee-saved + psp in CCS */
+    /* save callee-saved + psp in TCS */
     mrs ip, PSP
     stmia r0, {v1-v8, ip}
 
@@ -105,7 +104,7 @@ SECTION_FUNC(TEXT, __pendsv)
     movs.n r0, #_EXC_IRQ_DEFAULT_PRIO
     msr BASEPRI, r0
 
-    /* find out incoming context (fiber or task) */
+    /* find out incoming thread (fiber or task) */
 
     /* is there a fiber ready ? */
     ldr r2, [r1, #__tNANO_fiber_OFFSET]
@@ -116,12 +115,12 @@ SECTION_FUNC(TEXT, __pendsv)
      * else, the task is the thread we're switching in
      */
     itte ne
-	ldrne.w r0, [r2, #__tCCS_link_OFFSET]   /* then */
+	ldrne.w r0, [r2, #__tTCS_link_OFFSET]   /* then */
 	strne.w r0, [r1, #__tNANO_fiber_OFFSET] /* then */
 	ldreq.w r2, [r1, #__tNANO_task_OFFSET]  /* else */
 
     /* r2 contains the new thread */
-    ldr r0, [r2, #__tCCS_flags_OFFSET]
+    ldr r0, [r2, #__tTCS_flags_OFFSET]
     str r0, [r1, #__tNANO_flags_OFFSET]
     str r2, [r1, #__tNANO_current_OFFSET]
 
@@ -138,13 +137,13 @@ SECTION_FUNC(TEXT, __pendsv)
     str r3, [ip, #0]
 
     /* restore BASEPRI for the incoming thread */
-    ldr r0, [r2, #__tCCS_basepri_OFFSET]
+    ldr r0, [r2, #__tTCS_basepri_OFFSET]
     mov ip, #0
-    str ip, [r2, #__tCCS_basepri_OFFSET]
+    str ip, [r2, #__tTCS_basepri_OFFSET]
     msr BASEPRI, r0
 
-    /* load callee-saved + psp from CCS */
-    add r0, r2, #__tCCS_preempReg_OFFSET
+    /* load callee-saved + psp from TCS */
+    add r0, r2, #__tTCS_preempReg_OFFSET
     ldmia r0, {v1-v8, ip}
     msr PSP, ip
 
@@ -205,9 +204,9 @@ SECTION_FUNC(TEXT, __svc)
  * __pendsv all come from handling an interrupt, which means we know the
  * interrupts were not locked: in that case the BASEPRI value is 0.
  *
- * Given that _Swap() is called to effect a cooperative context context switch,
- * only the caller-saved integer registers need to be saved in the tCCS of the
- * outgoing context. This is all performed by the hardware, which stores it in
+ * Given that _Swap() is called to effect a cooperative context switch,
+ * only the caller-saved integer registers need to be saved in the TCS of the
+ * outgoing thread. This is all performed by the hardware, which stores it in
  * its exception stack frame, created when handling the svc exception.
  *
  * @return may contain a return value setup by a call to fiberRtnValueSet()
@@ -222,7 +221,7 @@ SECTION_FUNC(TEXT, _Swap)
 
     ldr r1, =_nanokernel
     ldr r2, [r1, #__tNANO_current_OFFSET]
-    str r0, [r2, #__tCCS_basepri_OFFSET]
+    str r0, [r2, #__tTCS_basepri_OFFSET]
 
     svc #0