[AMDGPU][NFC] Alter ComplexPattern types to be consistent with their uses

When used as a non-leaf node, TableGen does not currently use the type
of a ComplexPattern for type inference, which also means it does not
check it doesn't conflict with the use. This differs from when used as a
leaf value, where the type is used for inference. Fixing that
discrepancy is something I intend to upstream as a subsequent review.

AMDGPU currently has several ComplexPatterns that are used in contexts
where they're expected to be an iPTR, and where using an iPTR instead of
a fixed-width integer type matters. With my locally-patched TableGen,
none of these mismatches result in type contradictions, but do change
the patterns and cause various failures to select. These changes to the
ComplexPatterns' types reflect how they are actually used, result in
bit-for-bit identical TableGen output (without my local TableGen patch),
and ensure that with improved type inference AMDGPU's backend will
continue to work.

Reviewed By: arsenm

Differential Revision: https://reviews.llvm.org/D109032