riscv64: define instruction set features. am: 910c95fe2d am: 67db9154d5 am: 60d3c24526

Original change: https://android-review.googlesource.com/c/platform/art/+/2421275

Change-Id: I1151cec064c7154fa82058bdbef8ba03c8ad958e
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>