[AArch64] Make FeatureFuseAdrpAdd a tune feature

Update D120104 to add FeatureFuseAdrpAdd to Processor#TuneFeatures
instead of Processor#Features, similar to FeatureFuseAES, and matching
Tune*.

This enables FeatureFuseAdrpAdd for `clang -mcpu=xxx -mtune=generic` even
if xxx does not set FeatureFuseAdrpAdd.

Reviewed By: alexander-shaposhnikov, peter.smith

Differential Revision: https://reviews.llvm.org/D128787