[AMDGPU][MachineVerifier] Alignment check for fp32 packed math instructions

The fp32 packed math instructions are introduced in gfx90a.
If their vector register operands are not properly aligned, the
verifier should flag them. Currently, the verifier failed to
report it and the compiler ended up emitting a broken assembly.
This patch fixes that missed case in TII::verifyInstruction.

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D121794