AArch64: Add fma_reassoc_width [PR107413]

AArch64: Add fma_reassoc_width [PR107413]

Add a reassocation width for FMA in per-CPU tuning structures. Keep
the existing setting of 1 for cores with 2 FMA pipes (this disables
reassociation), and use 4 for cores with 4 FMA pipes.  This improves
SPECFP2017 on Neoverse V1 by ~1.5%.

gcc/
	PR tree-optimization/107413
	* config/aarch64/aarch64.cc (struct tune_params): Add
	fma_reassoc_width to all CPU tuning structures.
	(aarch64_reassociation_width): Use fma_reassoc_width.
	* config/aarch64/aarch64-protos.h (struct tune_params): Add
	fma_reassoc_width.