aarch64: Add -mtune=neoverse-512tvb

aarch64: Add -mtune=neoverse-512tvb

This patch adds an option to tune for Neoverse cores that have
a total vector bandwidth of 512 bits (4x128 for Advanced SIMD
and a vector-length-dependent equivalent for SVE).  This is intended
to be a compromise between tuning aggressively for a single core like
Neoverse V1 (which can be too narrow) and tuning for AArch64 cores
in general (which can be too wide).

-mcpu=neoverse-512tvb is equivalent to -mcpu=neoverse-v1
-mtune=neoverse-512tvb.

gcc/
	* doc/invoke.texi: Document -mtune=neoverse-512tvb and
	-mcpu=neoverse-512tvb.
	* config/aarch64/aarch64-cores.def (neoverse-512tvb): New entry.
	* config/aarch64/aarch64-tune.md: Regenerate.
	* config/aarch64/aarch64.c (neoverse512tvb_sve_vector_cost)
	(neoverse512tvb_sve_issue_info, neoverse512tvb_vec_issue_info)
	(neoverse512tvb_vector_cost, neoverse512tvb_tunings): New structures.
	(aarch64_adjust_body_cost_sve): Handle -mtune=neoverse-512tvb.
	(aarch64_adjust_body_cost): Likewise.