[AMDGPU] Add some missing always-uniform values.

This commit adds some missing intrinsics into the isAlwaysUniform list
for the AMDGPU backend.

Differential Revision: https://reviews.llvm.org/D56845

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@351562 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed