vidc:vdec: Clean extradata portion and invalidate whole buffer

This commit will ensure to clean the extradata portion in
output buffer changed by the CPU before sending the buffer
to Video hardware and invalidate the output buffer changed
by Video hardware before CPU access the buffer.

Change-Id: I05ea24fb381a164f6cfd520bd9071a94349ed2df
CRs-fixed: 366446
Signed-off-by: Maheshwar Ajja <majja@codeaurora.org>