ENGR00293132-1 pxp/v4l2: change memory alloc policy for PxP output buffer

ENGR00293132-1 pxp/v4l2: change memory alloc policy for PxP output buffer

In previous implementation, the memory allocation/free for PxP output buffer is
done each time v4l2 output device is opened/closed. This is not necessary and
may cause memory fragmentation issue after running many many times. Now we
re-allocate the memory for it only if the existing memory size is not sufficent
for new case.

Signed-off-by: Robby Cai <R63905@freescale.com>