Add assembler for riscv64, part 3. am: e7dd044ecf

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

Change-Id: I1be58243f3e586c2e3e4f2fce50fa0eb144f268c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>