AArch64: Add FULLY_PIPELINED_FMA to tune baseline

Add FULLY_PIPELINED_FMA to tune baseline - this is a generic feature that is
already enabled for some cores, but benchmarking it shows it is faster on all
modern cores (SPECFP improves ~0.17% on Neoverse V1 and 0.04% on Neoverse N1).

gcc:
	* config/aarch64/aarch64-tuning-flags.def (AARCH64_EXTRA_TUNE_BASE):
	Add AARCH64_EXTRA_TUNE_FULLY_PIPELINED_FMA.
	* config/aarch64/tuning_models/ampere1b.h: Remove redundant
	AARCH64_EXTRA_TUNE_FULLY_PIPELINED_FMA.
	* config/aarch64/tuning_models/neoversev2.h: Likewise.