doc: move cmsis rtos API docs to portability/

Move CMSIS RTOS API docs under portability to distinguish from
architecture and board porting.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>

doc/guides/index.rst

@@ -7,6 +7,7 @@ User and Developer Guides
    :maxdepth: 1
 
    getting-help.rst
+   portability/index.rst
    bluetooth/index.rst
    c_library
    ../README.rst

doc/guides/portability/index.rst

@@ -0,0 +1,18 @@
+.. _osal:
+
+OS Abstraction
+##############
+
+OS abstraction layers (OSAL) provide wrapper function APIs that
+encapsulate common system functions offered by any operating system.
+These APIs make it easier and quicker to develop for, and port code to
+multiple software and hardware platforms.
+
+These sections describe the software and hardware abstraction layers
+supported by the Zephyr RTOS.
+
+.. toctree::
+   :maxdepth: 1
+
+   cmsis_rtos_v1.rst
+   cmsis_rtos_v2.rst

doc/guides/porting/index.rst

@@ -12,5 +12,4 @@ API interfaces supported by Zephyr.
 
    arch.rst
    board_porting.rst
-   porting_to_zephyr.rst
    shields.rst

doc/guides/porting/porting_to_zephyr.rst

@@ -1,15 +0,0 @@
-.. _porting_to_zephyr:
-
-Porting Applications to Zephyr
-##############################
-
-This section describes standard API interfaces supported by Zephyr.
-Applications written using standard API interfaces are supposed to
-be OS agnostic. Supporting such APIs in Zephyr would make it easier
-to port those applications to Zephyr.
-
-.. toctree::
-   :maxdepth: 1
-
-   cmsis_rtos_v1.rst
-   cmsis_rtos_v2.rst