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

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

Change-Id: Ia6e5179f2aaad4065a2721436b098d9054219fa6
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>