Add wD constraint.

Add wD constraint.

This patch adds a new constraint ('wD') that matches the accumulator registers
that overlap with VSX registers 0..31 on power10.  Future patches will add the
support for a separate accumulator register class that will be used when the
support for dense math registes is added.

2024-03-19   Michael Meissner  <meissner@linux.ibm.com>

	* config/rs6000/constraints.md (wD): New constraint.
	* config/rs6000/mma.md (mma_disassemble_acc): Likewise.
	(mma_<vv>): Likewise.
	(mma_<avv>): Likewise.
	(mma_<pv>): Likewise.
	(mma_<apv>): Likewise.
	(mma_<vvi4i4i8>): Likewise.
	(mma_<avvi4i4i8>): Likewise.
	(mma_<vvi4i4i2>): Likewise.
	(mma_<avvi4i4i2>): Likewise.
	(mma_<vvi4i4>): Likewise.
	(mma_<avvi4i4>): Likewise.
	(mma_<pvi4i2): Likewise.
	(mma_<apvi4i2>): Likewise.
	(mma_<vvi4i4i4>): Likewise.
	(mma_<avvi4i4i4): Likewise.
	* config/rs6000/predicates.md (accumulator_operand): New predicate.
	* config/rs6000/rs6000.cc (rs6000_debug_reg_global): Print the register
	class for the 'wD' constraint.
	(rs6000_init_hard_regno_mode_ok): Set the 'wD' register constraint
	class.
	* config/rs6000/rs6000.h (enum r6000_reg_class_enum): Add element for
	the 'wD' constraint.
	* doc/md.texi (PowerPC constraints): Document the 'wD' constraint.