camera: Modify the camera event interface.

- The current camera event interface is limited
  to 64 bytes. This restricts the interaction
  between the driver and the  userspace since
  the current structures used are already using
  the entire 64 bytes. Hence change the interface
  to overcome this limitation and accomodate more
  usecases(eg: postprocessing for multiplanar formats)
- Renamed the event structure to a more generic
  name.

Change-Id: Id3c635e2652491da4efd8fe34c32d63464b83755
Signed-off-by: Kiran Kumar H N <hurlisal@codeaurora.org>