[media] tvp5150: Restructure version detection

Move the version detection code to a separate function and restructure
it to prepare for TVP5151 support.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>