[media] s5p-mfc: use MFC_BUF_FLAG_EOS to identify last buffers in decoder capture queue

MFC driver never delivered EOS event to apps feeding constantly its capture
buffer with fresh buffers. The patch fixes it by marking last buffers
returned by MFC with MFC_BUF_FLAG_EOS flag and firing EOS event on
de-queuing such buffers.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>