AMDGPU: Add atomic_inc + atomic_dec intrinsics

These are different than atomicrmw add 1 because they have
an additional input value to clamp the result.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@266074 91177308-0d34-0410-b5e6-96231b3b80d8
12 files changed