[AArch64] Combine SEXT_INREG(CSET) to CSETM. (#156429)
Add the following patterns to performSignExtendInRegCombine:
* SIGN_EXTEND_INREG (CSEL 0, 1, cc), i1 --> CSEL 0, -1, cc
* SIGN_EXTEND_INREG (CSEL 1, 0, cc), i1 --> CSEL -1, 0, cc
The combined forms can be matched to a CSETM.
