DO NOT MERGE: Send an exit broadcast on gear reversal.

Re-use the existing driving exit intent for gear reversal.
Add an intent extra for indicating gear reversal.

Bug: 151109459
Test: inject gear reversal VHAL event and SUW exits
Signed-off-by: Julius D'souza <jdsouza@google.com>
Change-Id: I1071ab5154f2c0d8bc6f72a7ba90e03cd18b8405