media: vimc: embed the pads of entities in the entities' structs

since the pads array is of known small size, there is no reason to
allocate it separately. Instead, it is embedded in the entity struct.
This also conforms to the media controller doc:
'Most drivers will embed the pads array in a driver-specific structure,
avoiding dynamic allocation.'

Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@collabora.com>
[hverkuil-cisco@xs4all.nl: remove unused vimc_pads_init()]
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>