[AMDGPU] Fix wide spills

[piotr]

Summary

Update spill code to account for new vector types with
bit widths: 288, 320, 352, 384.

Related to D138205.

[arsenm]

Should also test AGPR

llvm/test/CodeGen/AMDGPU/spill288.mir

3–4

Should test with gfx90a to cover the AGPRs

126

Can you also test AGPR

[piotr]

Thanks - the extra set of tests has uncovered another issue in code.

[piotr]

Updating patch to address two more issues detected by running tests in debug mode:

• wrong opcodes used in getVGPRSpillSaveOpcode in the original patch
• tests using insufficient spill slot size in my patch