V4L/DVB (4597): Improve resolution limit enforcements in pvrusb2

The pvrusb2 driver resolution limits are now programmed the following
way, based on empirical measurements of the hardware:
  Vertical   max: 480 for NTSC, 576 otherwise
  Vertical   min: 75 for 24xxx, 17 otherwise
  Horizontal max: 720
  Horizontal min: 720 for 24xxx, 19 otherwise

Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>