aarch64: Add support for Ampere-1A (-mcpu=ampere1a) CPU

aarch64: Add support for Ampere-1A (-mcpu=ampere1a) CPU

This patch adds support for Ampere-1A CPU:
 - recognize the name of the core and provide detection for -mcpu=native,
 - updated extra_costs,
 - adds a new fusion pair for (A+B+1 and A-B-1).

Ampere-1A and Ampere-1 have more timing difference than the extra
costs indicate, but these don't propagate through to the headline
items in our extra costs (e.g. the change in latency for scalar sqrt
doesn't have a corresponding table entry).

gcc/ChangeLog:

	* config/aarch64/aarch64-cores.def (AARCH64_CORE): Add ampere1a.
	* config/aarch64/aarch64-cost-tables.h: Add ampere1a_extra_costs.
	* config/aarch64/aarch64-fusion-pairs.def (AARCH64_FUSION_PAIR):
	Define a new fusion pair for A+B+1/A-B-1 (i.e., add/subtract two
	registers and then +1/-1).
	* config/aarch64/aarch64-tune.md: Regenerate.
	* config/aarch64/aarch64.cc (aarch_macro_fusion_pair_p): Implement
	idiom-matcher for the new fusion pair.
	* doc/invoke.texi: Add ampere1a.