V4L/DVB (4672): Frame format enumeration (1/2)

Add VIDIOC_ENUM_FRAMESIZES and VIDIOC_ENUM_FRAMEINTERVALS ioctls to enumerate 
supported frame sizes and frame intervals.

Signed-off-by: Martin Rubli <martin.rubli@epfl.ch>
Signed-off-by: Laurent Pinchart <laurent.pinchart@skynet.be>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>