[media] vpif_cap/disp: Cleanup, improved comments

Signed-off-by: Mats Randgaard <mats.randgaard@cisco.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Murali Karicheri <mkaricheri@gmail.com>
Acked-by: Vaibhav Hiremath <hvaibhav@ti.com>
Acked-by: Manjunath Hadli <manjunath.hadli@ti.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>