This is directly available in TargetInstrInfo

Both conceptually belong to the same subtarget, so it should not
be necessary to pass in the context TargetRegisterInfo to any
TargetInstrInfo member. Add this reference so those superfluous
arguments can be removed.

Most targets placed their TargetRegisterInfo as a member
in TargetInstrInfo. A few had this owned by the TargetSubtargetInfo,
so unify all targets to look the same.

.. to isReMaterializableImpl.  The "Really" naming has always been
awkward, and we're working towards removing the "Trivial" part now,
so go ehead and remove both pieces in a single rename.

Note that this doesn't change any aspect of the current
implementation; we still "mostly" only return instructions which
are trivial (meaning no virtual register uses), but some targets
do lie about that today.

This will make it possible for tablegen to make subtarget
dependent decisions without adding new arguments to every
target.

---------

Co-authored-by: Sergei Barannikov <barannikov88@gmail.com>

This patch updates PPCInstrInfo::copyPhysReg to support DMR and WACC
register classes and extends the PPCVSXCopy pass to handle specific WACC
copy patterns.

Add spilling and restoring of DMR registers.

For cpu=future, acc registers no longer overlap VSRs and are prefixed
with `dm`. The original, xxmfacc/xxmtacc instructions are now extended
menemonics to it's dm* equivalents.