arm: enable Cortex-A710 CPU

This patch is adding support for Cortex-A710 CPU in Arm.

bfd/

	* cpu-arm.c (processors): Add cortex-a710.

gas/

	* NEWS: Update docs.
	* config/tc-arm.c (arm_cpus): Add cortex-a710 to -mcpu.
	* doc/c-arm.texi: Update docs.
	* testsuite/gas/arm/cpu-cortex-a710.d: New test.