doc: add the ARC part for release 2.3

add the ARC processor related part for release 2.3

Signed-off-by: Wayne Ren <[email protected]>

Author: Wayne Ren

doc/releases/release-notes-2.3.rst

@@ -167,7 +167,15 @@ Architectures
 
 * ARC:
 
-  * <TBD>
+  * Changed to automatic generation of privilege stack for ARC MPU V2 to
+    avoid the potential waste of memory When USERSPACE is configured
+  * Enhanced runtime programming for the MPU v3 by making the gap-filling
+    of kernel memory a user-configurable feature
+  * Refactored the thread switch code in epilogue of irq and exception
+  * Refactored the assembly codes for better maintenance
+  * Fixed the behavior of ARC timer driver
+  * Fixed the behavior of ARC SMP
+  * Fixed the wrong configurations of ARC boards in Kconfig and DTS
 
 * ARM: