greybus: vibrator: integrate runtime pm

Integrate greybus drivers with the Linux Kernel RuntimePM framework
for vibrator driver.

Testing Done: AP side (kernel) can control the vibrator driver with
suspend and resume.

Signed-off-by: Ann Chen <chen_ann@projectara.com>
Reviewed-by: David Lin <dtwlin@google.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>