[media] s5p-fimc: Add media entity initialization

Add intialization of the media entities for video capture
and mem-to-mem video nodes. The mem-to-mem entity has no pads
whereas the capture entity has single sink pad.
Also clean up the video node naming for consistency.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>