msm: vidc: Remove dependency on PREPARE_BUF

Firmware does not have any hard requirement for pre-announcement
of input/output buffers. So, remove this driver restriction.

Change-Id: I97786d69cd12c3f162f9a00465c7b3f71d69c06c
Signed-off-by: Vinay Kalia <vkalia@codeaurora.org>