[AArch64][GlobalISel] Legalize 32-bit + narrow G_SMULO + G_UMULO

SDAG lowers 32-bit and 64-bit G_SMULO + G_UMULO. We were missing the 32-bit
case.

For other sizes, make the 0th type a power of 2 and clamp it to either 32 bits
or 64 bits.

Right now, this will allow us to handle narrow types (e.g. s4, s24, etc.). The
LegalizerHelper doesn't support narrowing G_SMULO or G_UMULO right now. I think
we want clamping behaviour either way, so we might as well include it now to
be explicit.

Differential Revision: https://reviews.llvm.org/D108240