riscv64: add initial support for ART.

The only supported mode is the switch interpreter. JNI transitions are
not implemented yet (not even generic JNI trampoline), therefore it is
impossible to run even a simple hello world test (because it requires
loading Java libraries and initializing classes in them, many of which
call native methods). The only passing ART test is 000-nop.

Test: run ART test 000-nop on a Linux RISC-V VM:
  lunch aosp_riscv64-userdebug

  export ART_TEST_SSH_USER=ubuntu
  export ART_TEST_SSH_HOST=localhost
  export ART_TEST_SSH_PORT=10001
  export ART_TEST_ON_VM=true

  . art/tools/buildbot-utils.sh
  art/tools/buildbot-build.sh --target

  # Create, boot and configure the VM.
  art/tools/buildbot-vm.sh create
  art/tools/buildbot-vm.sh boot
  art/tools/buildbot-vm.sh setup-ssh  # password: 'ubuntu'

  art/tools/buildbot-cleanup-device.sh
  art/tools/buildbot-setup-device.sh
  art/tools/buildbot-sync.sh

  art/test.py --target -r --no-prebuild --ndebug --no-image \
    --64 --interpreter 000-nop

Co-authored-by: Lifang Xia <lifang_xia@linux.alibaba.com>
Change-Id: Iac267525527901b74e863cb8c72ddcf0789e8a5d
27 files changed