V4L/DVB (7257): cx88: Add xc2028/3028 boards

This patch ports a patch from Markus Rechberger to work with tuner-xc2028.
It adds entries for several cx88 boards with xc2038/3028 tuners.

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>