[AArch64] Fix pairing different types of registers when computing CSRs. (#66642)

If a function has odd number of same type of registers to save, and the
calling convention also requires odd number of such type of CSRs, an FP
register would be accidentally marked as saved when producePairRegisters
returns true.

This patch also fixes the AArch64LowerHomogeneousPrologEpilog pass not
handling AArch64::NoRegister; actually this pass must be fixed along
with the register pairing so i can write a test for it.