TargetInstrInfo now directly holds a reference to TargetRegisterInfo
and does not need TRI passed in anywhere.

This is a low level utility to parse the MCInstrInfo and should
not depend on the state of the function.

getPointerRegClass is a layering violation. Its primary purpose
is to determine how to interpret an MCInstrDesc's operands RegClass
fields. This should be context free, and only depend on the subtarget.
The model of this is also wrong, since this should be an
instruction / operand specific property, not a global pointer class.
Remove the the function argument to help stage removal of this hook
and avoid introducing any new obstacles to replacing it.

The remaining uses of the function were to get the subtarget, which
TargetRegisterInfo already belongs to. A few targets needed new
subtarget derived properties copied there.

If a copy exists between creation of a crbit and a spill, machine-cp
may delete the copy since it seems unaware of the relation between a cr
and crbit. A fix was previously made for the generic ppc64 lowering. It
should be applied to the pwr9 and pwr10 variants too.

Likewise, relax and extend the pwr8 test to verify pwr9 and pwr10
codegen too.

This fixes #143989.

Simpliy handling for spilling of acc reg with stx by removing explicit
register arithmetic and clean up code gen for register mapping used in
stxvp spilling.

Relanding: https://github.com/llvm/llvm-project/pull/142220

…ling (#142220)"

This reverts commit edf636afe405ff90da7bf1834aa334bd52bc861e.
checked in wrong branch.

Remove explicit register arithmetic from spilling ACC and STXVP code.

Add spilling and restoring of DMR registers.

Move all if-else conditions into a switch stmt for handling spills.