[RISCV] Remove CalleeSavedInfo for Zcmp/save-restore-libcalls registers (#79535)

Registers that are pushed/popped by Zcmp or libcalls have pre-defined
frame indices that are never allocated in MachineFrameInfo. They're
being used throughout PEI, but the rest of codegen doesn't work that way
and expects each frame index to be a valid index in MFI.

This patch keeps it local to PEI and removes them from the
CalleeSavedInfo list at the end of the pass.

Before this pass, any MIR testing post-PEI is broken and asserts (see
issue #79491).