v2: Add missing PROFILE feature flag.

This patch adds support for the Cortex-A720 CPU to GCC.

No regressions on aarch64-none-elf.

Ok for master?

gcc/ChangeLog:

         * config/aarch64/aarch64-cores.def (AARCH64_CORE): Add Cortex-
	A720 CPU.
         * config/aarch64/aarch64-tune.md: Regenerate.
         * doc/invoke.texi: Document Cortex-A720 CPU.