Add features for automotive usecases.

1. Add clock to metadata - If the CAR does not have a clock (no network
or bad clock) then Radio RDS could be used as a proxy.
2. Add support for emergency announcement - If the CAR wants to make an
emergency announcement.
    2.1 Add support for callbacks.

Bug: b/24807501
Bug: b/22701655

Change-Id: Ie5ada889bb6dfc4a2c1b02fc1db2d48d6899bcde
(cherry picked from commit 5768372922fbdfa47afef5bb414c69d606e7c1d2)
1 file changed