riscv64: Add entrypoints for unresolved fields.

And enable `*Unresolved*` instructions in codegen.

Test: m  # aosp_cf_riscv64_phone-userdebug
Test: # Edit `run-test` to disable checker, then
      testrunner.py --target --64 --ndebug --optimizing
      # Ignore 3 pre-existing failures.
Bug: 283082089
Change-Id: I04f23161d96f9eefdbe1e3b17ed0f7ae695deb07
7 files changed