msm: vidc: Remove the redundant command handling

Both dec_cmd and enc_cmd are for the same purpose and in two
different files. Having them duplicate can cause mismatch of
handling commands. Hence combine them into single function to
remove the unnecessary code.

Change-Id: I788b3653e3eb4e5e8d019baeef0fabfb9d1d6e56
Signed-off-by: Praneeth Paladugu <ppaladug@codeaurora.org>