aarch64: enable Ampere-1 CPU

aarch64: enable Ampere-1 CPU

This adds support and a basic turning model for the Ampere Computing
"Ampere-1" CPU.

The Ampere-1 implements the ARMv8.6 architecture in A64 mode and is
modelled as a 4-wide issue (as with all modern micro-architectures,
the chosen issue rate is a compromise between the maximum dispatch
rate and the maximum rate of uops issued to the scheduler).

This adds the -mcpu=ampere1 command-line option and the relevant cost
information/tuning tables for the Ampere-1.

gcc/ChangeLog:

	* config/aarch64/aarch64-cores.def (AARCH64_CORE): New Ampere-1	core.
	* config/aarch64/aarch64-tune.md: Regenerate.
	* config/aarch64/aarch64-cost-tables.h: Add extra costs for Ampere-1.
	* config/aarch64/aarch64.c: Add tuning structures for Ampere-1.
	* doc/invoke.texi: Add documentation for Ampere-1 core.