AP_Camera: Relocate feedback messages.

Relocated feedback message content according to Mavlink libraries
(msg_camera_feedback).
Included camera_flags for future developments.
This doesn't match the parameters of the camera_feedback message. https://github.com/diydrones/ardupilot/blob/master/libraries/GCS_MAVLink/include/mavlink/v1.0/ardupilotmega/mavlink_msg_camera_feedback.h#L234