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

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

Change-Id: I0d50072f46484de371e33f4579a291fb898393d7
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>