[AArch64][docs] Add release notes for FUJITSU-MONAKA support

Adds release notes for the FUJITSU-MONAKA support introduced in PR #118432.
These notes were missing from the original PR.

Author: kinoshita-fj

clang/docs/ReleaseNotes.rst

@@ -977,6 +977,10 @@ Arm and AArch64 Support
   in leaf functions after enabling ``-fno-omit-frame-pointer``, you can do so by adding
   the ``-momit-leaf-frame-pointer`` option.
 
+- Support has been added for the following processors (-mcpu identifiers in parenthesis):
+
+  * FUJITSU-MONAKA (fujitsu-monaka)
+
 Android Support
 ^^^^^^^^^^^^^^^
 

llvm/docs/ReleaseNotes.md

@@ -131,6 +131,8 @@ Changes to the AArch64 Backend
 * Assembler/disassembler support has been added for Armv9.6-A (2024)
   architecture extensions.
 
+* Added support for the FUJITSU-MONAKA CPU.
+
 Changes to the AMDGPU Backend
 -----------------------------