doc: release: 2.7: Add release note for aarch32

Mention the addition of MPU support for Cortex-R.

Signed-off-by: Bradley Bolen <[email protected]>

Author: Bradley Bolen

doc/releases/release-notes-2.7.rst

@@ -156,6 +156,7 @@ Architectures
      * Updated CMSIS version to 5.8.0
      * Added support for FPU in QEMU for Cortex-M, allowing to build and execute
        tests in CI with FPU and FPU_SHARING options enabled.
+     * Added MPU support for Cortex-R
 
 
   * AARCH64