Add assembler for riscv64, part 4. am: 5d567e508e am: 013a957d48

Original change: https://android-review.googlesource.com/c/platform/art/+/2598686

Change-Id: I70b3654d8ae657232525dbf2135d100223008ced
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>