[ARM]: Add Cortex-R52 target

This patch adds Cortex-R52, the new ARM real-time processor.
Cortex-R52 implements the ARMv8-R architecture.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@283543 91177308-0d34-0410-b5e6-96231b3b80d8