AMDGPU/GlobalISel: Prepare some tests for store selection

Mostsly these would fail due to trying to use SI with a flat
operation. Implementing global loads with MUBUF is more work than
flat, so these won't be handled in the initial load selection.

Others fail because store of s64 won't initially work, as the current
set of patterns expect everything to be turned into v2i32.

llvm-svn: 365493