PowerPC: Vector Instructions for Deeply Compressed Weight for AI (RFC02691)

opcodes/
	* ppc-opc.c: (VXSEL5, VXSEL4, VXSEL3, VXSEL2, UIMM1): New defines.
	(powerpc_opcodes): <vucmprhn, vucmprln, vucmprhb, vucmprlb,
	vucmprhh, vucmprlh, vupkhsntob, vupklsntob, vupkint4tobf16,
	vupkint8tobf16, vupkint4tofp32, vupkint8tofp32>: New instructions.

gas/
	* gas/testsuite/gas/ppc/future.s: Add new testcases.
	* gas/testsuite/gas/ppc/future.d: Likewise.