[AArch64] Add support for Neoverse N1

[AArch64] Add support for Neoverse N1

This patch adds support for the Neoverse N1 CPU [1]. This was supported in GCC earlier through the codename Ares,
which it now replaces. -mcpu=ares is still accepted as there's been a binutils release supporting it,
but the internal structures are renamed to use Neoverse N1-related identifiers.

Bootstrapped and tested on aarch64-none-linux-gnu.

	* config/aarch64/aarch64.c (ares_tunings): Rename to...
	(neoversen1_tunings): ... This.
	* config/aarch64/aarch64-cores.def (ares): Change tuning to the above.
	(neoverse-n1): New CPU.
	* config/aarch64/aarch64-tune.md: Regenerate.
	* doc/invoke.txt (AArch64 Options): Document neoverse-n1.

From-SVN: r269099