[media] davinci vpbe: VENC( Video Encoder) implementation

This patch adds the VENC or the Video encoder, which is responsible
for the blending of all source planes and timing generation for Video
modes like NTSC, PAL and other digital outputs. the VENC implementation
currently supports COMPOSITE and COMPONENT outputs and NTSC and PAL
resolutions through the analog DACs. The venc block is implemented
as a subdevice, allowing for additional external and internal encoders
of other kind to plug-in.

Signed-off-by: Manjunath Hadli <manjunath.hadli@ti.com>
Acked-by: Muralidharan Karicheri <m-karicheri2@ti.com>
Acked-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>