[InstrInfo] Use 64-bit immediates for analyzeCompare() (NFCI)

The backend generally uses 64-bit immediates (e.g. what
MachineOperand::getImm() returns), so use that for analyzeCompare()
and optimizeCompareInst() as well. This avoids truncation for
targets that support immediates larger 32-bit. In particular, we
can avoid the bugprone value normalization hack in the AArch64
target.

This is a followup to D108076.

Differential Revision: https://reviews.llvm.org/D108875