[AArch64] Add support for Fujitsu A64FX

A64FX is an Armv8.2-A CPU used in FUJITSU Supercomputer
PRIMEHPC FX1000, PRIMEHPC FX700, and supercomputer Fugaku.

https://www.fujitsu.com/global/products/computing/servers/supercomputer/specifications/

Differential Revision: https://reviews.llvm.org/D75594