unified/arm: add unified kernel support for ARM arch

The ARM architecture port is fitted with support for the unified kernel,
namely:

- the interrupt/exception exit code now pends PendSV if the current
  thread is not a coop thread and if the scheduler is not locked

- fiber_abort is replaced by k_thread_abort(), which takes a thread ID
  as a parameter (i.e. does not only operate on the current thread)

- the _nanokernel.flags cache of _current.flags is not used anymore
  (could be a source of bugs) and is not needed in the scheduling algo

- there is no 'task' field in the _nanokernel anymore: PendSV not calls
  _get_next_ready_thread instead

- the _nanokernel.fiber field is replaced by a more sophisticated
  ready_q, based on the microkernel's priority-bitmap-based one

- thread initialization initializes new fields in the tcs, and does not
  initialize obsolete ones

- nano_private includes nano_internal.h from the unified directory

- The FIBER, TASK and PREEMPTIBLE flags do not exist anymore: the thread
  priority drives the behaviour

- the tcs uses a dlist for queuing in both ready and wait queues instead
  of a custom singly-linked list

- other new fields in the tcs include a schedule-lock count, a
  back-pointer to init data (when the task is static) and a pointer to
  swap data, needed when a thread pending on _Swap() must be passed more
  then just one value (e.g. k_stack_pop() needs an error code and data)

- the 'fiber' and 'task' fields of _nanokernel are replaced with an O(1)
  ready queue (taken from the microkernel)

- fiberRtnValueSet() is aliased to _set_thread_return_value since it
  also operates on preempt threads now

- _set_thread_return_value_with_data() sets the swap_data field in
  addition to a return value from _Swap()

- convenience aliases are created for shorter names:

  - _current is defined as _nanokernel.current
  - _ready_q is defined as _nanokernel.ready_q

- _Swap() sets the threads's return code to -EAGAIN before swapping out
  to prevent timeouts to have to set it (solves hard issues in some
  kernel objects).

Change-Id: I36c03c362bc2908dae064ec67e6b8469fc573983
Signed-off-by: Benjamin Walsh <benjamin.walsh@windriver.com>

arch/arm/core/exc_exit.S

@@ -37,6 +37,10 @@ GTEXT(_ExcExit)
 GTEXT(_IntExit)
 GDATA(_nanokernel)
 
+#ifdef CONFIG_KERNEL_V2
+GTEXT(__must_switch_threads)
+#endif
+
 #if CONFIG_GDB_INFO
   #define _EXIT_EXC_IF_FIBER_PREEMPTED beq _ExcExitWithGdbStub
 #else
@@ -92,6 +96,31 @@ SECTION_SUBSEC_FUNC(TEXT, _HandlerModeExit, _ExcExit)
 
     ldr r1, =_nanokernel
 
+#ifdef CONFIG_KERNEL_V2
+	ldr r1, [r1, #__tNANO_current_OFFSET]
+
+	ldr r2, [r1, #__tTCS_prio_OFFSET]
+	ldr r3, [r1, #__tTCS_sched_locked_OFFSET]
+
+	/* coop thread ? do not schedule */
+	cmp r2, #0
+	it lt
+	  bxlt lr
+
+	/* scheduler locked ? do not schedule */
+	cmp r3, #0
+	it gt
+	  bxgt lr
+
+	push {lr}
+	blx __must_switch_threads
+	pop {lr}
+	cmp r0, #0
+	it eq
+	  bxeq lr
+
+#else
+
     /* is the current thread preemptible (task) ? */
     ldr r2, [r1, #__tNANO_flags_OFFSET]
     ands.w r2, #PREEMPTIBLE
@@ -102,6 +131,8 @@ SECTION_SUBSEC_FUNC(TEXT, _HandlerModeExit, _ExcExit)
     cmp r2, #0
     _EXIT_EXC_IF_FIBER_NOT_READY
 
+#endif
+
     /* context switch required, pend the PendSV exception */
     ldr r1, =_SCS_ICSR
     ldr r2, =_SCS_ICSR_PENDSV