[AArch64] Enable RAS 1.1 system registers in all AArch64

Some use cases (e.g. kernel devs) have strict requirements to only enable
features available with -march=armv8-a, e.g. no armv8.1-a. Enabling RAS 1.1 in
all AArch64 means they can consider to support it.

Bear in mind that the first versions of the Armv8 architecture still do not
support RAS 1.1. This patch only lets devs write code with the user-friendly
register mnemonic instead of the ugly generic S<op0>_<op1>_<Cn>_<Cm>_<op2>.
They still need to place runtime checks to make sure that the CPU to run on
supports RAS 1.1.

Differential Revision: https://reviews.llvm.org/D90594