[media] xc4000: handle dib0700 broken i2c stretching

It was confirmed by DibCom that i2c stretching is broken in the i2c master
on the dib7700.  So we need to put a hack into the xc4000 driver to not
complain in certain very specific cases where we know i2c stretching occurs.

Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>