msm: vidc: Introduce ETB flag for Enc Superframe handling

Driver will internally produce subframe flag for all ETB of
a Superframe to firmware (except last ETB). Firmware will
propagate subframe flag to FBD. Driver client will receive
multiple FBDs with subframe flag for single Superframe ETB
(except last FBD). This subframe flag indicates that more
FBD expected for same input.

Change-Id: I627123ee2500dd7846363d8b819c3fa56234a494
Signed-off-by: Akshata Sahukar <asahukar@codeaurora.org>