Add assembler for riscv64, part 3. am: e7dd044ecf am: 6d4c064043 am: dc71310556

Original change: https://android-review.googlesource.com/c/platform/art/+/2596790

Change-Id: I9e1656e2d7d43a7b870f88a38fccca926276035e
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>