Revert "[ARM] Cleanup ARM CGP isSupportedValue"

This reverts r342395 as it caused error

> Argument value type does not match pointer operand type!
>   %0 = atomicrmw volatile xchg i8* %_Value1, i32 1 monotonic, !dbg !25
>  i8in function atomic_flag_test_and_set
> fatal error: error in backend: Broken function found, compilation aborted!

on bot http://green.lab.llvm.org/green/job/clang-stage1-configure-RA/

More details are available at https://reviews.llvm.org/D52080

llvm-svn: 342431