[Driver] Expose getARMCPUForMArch() function in the Driver API; NFC.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@212666 91177308-0d34-0410-b5e6-96231b3b80d8
Cleanup. No functionality change.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@212667 91177308-0d34-0410-b5e6-96231b3b80d8