Radio features for Automotive usecase.

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: Ib3131de03a022181559fd31da6701d9d3fa8698d
(cherry picked from commit 659688a129189f2a9aa353ddf9e107d5f293c4ca)