[AArch64][Clang] Adjust default features for v8.9-A/v9.4-A in clang driver

Update the clang driver to include the following features as default for
the v8.9-A/v9.4-A architecture versions:

* FEAT_SPECRES2
* FEAT_CSSC
* FEAT_RASv2

Patch by Sam Elliott.

Reviewed By: lenary, tmatheson

Differential Revision: https://reviews.llvm.org/D141404