AMDGPU: Minor cleanups to help with f16 support
AMDGPU: Minor cleanups to help with f16 support

The main change is inverting the condition for the
operand class classes so that VT.Size == 16 uses VGPR_32
instead of 64.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@245764 91177308-0d34-0410-b5e6-96231b3b80d8

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