[AMDGPU] Inline asm - added i16, half and i128 types support

AMDGPU inline assembler support i16, half and i128 typed variables in constraints, but they were reported as error.
Needed to fix https://github.com/RadeonOpenCompute/ROCm/issues/341,
e.g. to be able to load with global_load_dwordx4 to a 128bit integer variable

Differential Revision: https://reviews.llvm.org/D44920

llvm-svn: 334301