[ARM] Add Cortex-M55 Support for clang and llvm

This patch upstreams support for the ARM Armv8.1m cpu Cortex-M55.

In detail adding support for:

 - mcpu option in clang
 - Arm Target Features in clang
 - llvm Arm TargetParser definitions

details of the CPU can be found here:
https://developer.arm.com/ip-products/processors/cortex-m/cortex-m55

Reviewers: chill

Reviewed By: chill

Subscribers: dmgreen, kristof.beyls, hiraditya, cfe-commits,
llvm-commits

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D74966