[media] s5p-mfc: Add support for VP8 encoder

MFC v7 supports VP8 encoding and this patch adds support
for it in the driver.

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 <m.chehab@samsung.com>