riscv64: Add "Zbb" sign-/zero-extension to assembler. am: 7a8b55945e am: d9f607933b

Original change: https://android-review.googlesource.com/c/platform/art/+/2965283

Change-Id: I9c103ea502305a525cddf2469ef85a9bbf204890
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>