[media] s5p-mfc: Update v6 encoder buffer alloc

MFC v6 needs minimum number of output buffers to be queued
for encoder depending on the stream type and profile.
The patch modifies the driver so that encoding cannot be
started with lesser number of OUTPUT buffers than required.
This also fixes the crash happeninig during multi instance
encoder-decoder simultaneous run due to memory allocation
happening from interrupt context.

Signed-off-by: Arun Kumar K <arun.kk@samsung.com>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>