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

No regressions on aarch64-none-elf.

Ok for binutils-master?

bfd/ChangeLog:

	* cpu-aarch64.c: Add Cortex-A720.

gas/ChangeLog:

	* NEWS: Update docs.
	* config/tc-aarch64.c: Add Cortex-A720.
	* doc/c-aarch64.texi: Update docs.
	* testsuite/gas/aarch64/cpu-cortex-a720.d: New test.

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