[RISCV] Teach RISCVMatInt about cases where it can use LUI+SLLI to replace...

[RISCV] Teach RISCVMatInt about cases where it can use LUI+SLLI to replace LUI+ADDI+SLLI for large constants.

If we need to shift left anyway we might be able to take advantage
of LUI implicitly shifting its immediate left by 12 to cover part
of the shift. This allows us to use more bits of the LUI immediate
to avoid an ADDI.

isDesirableToCommuteWithShift now considers compressed instruction
opportunities when deciding if commuting should be allowed.

I believe this is the same or similar to one of the optimizations
from D79492.

Reviewed By: luismarques, arcbbb

Differential Revision: https://reviews.llvm.org/D105417