Combine patterns for p10 load-cmpi fusion

This patch adds the first batch of patterns to support p10 fusion. These
will allow combine to create a single insn for a pair of instructions
that power10 can fuse and execute. These particular fusion pairs have the
requirement that only cr0 can be used when fusing a load with a compare
immediate of -1/0/1 (if signed) or 0/1 (if unsigned), so we want combine
to put that requirement in, and if it doesn't work out the splitter
can change it back into 2 insns so scheduling can move them apart.

The patterns are generated by a script genfusion.pl and live in new file
fusion.md. This script will be expanded to generate more patterns for
fusion.

This also adds option -mpower10-fusion which defaults on for power10 and
will gate all these fusion patterns. In addition I have added an
undocumented option -mpower10-fusion-ld-cmpi (which may be removed later)
that just controls the load+compare-immediate patterns. I have made
these default on for power10 but they are not disallowed for earlier
processors because it is still valid code. This allows us to test the
correctness of fusion code generation by turning it on explicitly.

gcc/ChangeLog:

	* config/rs6000/genfusion.pl: New script to generate
	define_insn_and_split patterns so combine can arrange fused
	instructions next to each other.
	* config/rs6000/fusion.md: New file, generated fused instruction
	patterns for combine.
	* config/rs6000/predicates.md (const_m1_to_1_operand): New predicate.
	(non_update_memory_operand): New predicate.
	* config/rs6000/rs6000-cpus.def: Add OPTION_MASK_P10_FUSION and
	OPTION_MASK_P10_FUSION_LD_CMPI to ISA_3_1_MASKS_SERVER and
	POWERPC_MASKS.
	* config/rs6000/rs6000-protos.h (address_is_non_pfx_d_or_x): Add
	prototype.
	* config/rs6000/rs6000.c (rs6000_option_override_internal):
	Automatically set OPTION_MASK_P10_FUSION and
	OPTION_MASK_P10_FUSION_LD_CMPI if target is power10.
	(rs600_opt_masks): Allow -mpower10-fusion
	in function attributes.
	(address_is_non_pfx_d_or_x): New function.
	* config/rs6000/rs6000.h: Add MASK_P10_FUSION.
	* config/rs6000/rs6000.md: Include fusion.md.
	* config/rs6000/rs6000.opt: Add -mpower10-fusion
	and -mpower10-fusion-ld-cmpi.
	* config/rs6000/t-rs6000: Add dependencies involving fusion.md.