[AMDGPUHSAMetadataStreamer] Do not assume ABI alignment for pointers

AMDGPUHSAMetadataStreamer currently assumes that pointer arguments
without align attribute have ABI alignment of the pointee type.
This is incompatible with opaque pointers, but also plain incorrect:
Pointer arguments without explicit alignment have alignment 1. It is
the responsibility of the frontent to add correct align annotations.

Differential Revision: https://reviews.llvm.org/D118229