- Add the v9p support for arm platform.
- Add an option `-f` to set the shared directory on the host machine to
`do-qemuarm`.
- For example, to use the v9p dir sharing, run the script as:
```
# under `lk/` run the follow command will share the current
# directory `lk/` within LK vm as VirtIO 9p device
scripts/do-qemuarm -f .
```
Signed-off-by: Cody Wong <codycswong@google.com>