msm: vidc: Consolidate v4l2 control logic in driver

There was code duplication for v4l2 control setup in
decoder and encoder. This change tries to cut down on
the code duplication and makes common functionality
available for both decoder and encoder.

Change-Id: I8cb54297e82ca8161bea5248dce5289f7eda03c5
Signed-off-by: Arun Menon <avmenon@codeaurora.org>