V4L/DVB (9751): em28xx: card description cleanups

Remove unused em28xx_board.vchannels and em28xx.video_channels.
Also, .is_em2800 = 0 is not needed, as all data is zeroed by kernel loader.

The table also included a notice that svideo weren't test on Hauppauge
USB2. Remove this notice, since this input also works properly.

Also, it does some whitespace cleanups.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>