msm: vidc: Update minimum decoder output buffer count

For video decoder, minimum output buffer count returned by firmware
might not be sufficient for smooth playback performance. This commit
updates the minimum output buffer count for video decoder.

b/24065713

Change-Id: I240020e4b8e5f185c37af538cc1bd5426b9d8b04
Signed-off-by: Ashray Kulkarni <ashrayk@codeaurora.org>