V4L/DVB (13178): gspca: Add support for Winbond W9967CF and W9968CF camera's

This patch adds support to gspca for the Winbond W9967CF and W9968CF
camera's. This is mostly a port of the existing v4l1 driver to gspca
(making it v4l2). But this also features fixes to the bitbanging i2c code
(send a nack not an ack after reading the last byte of a transfer), which
gets rid of the weird errors which were being seen there, and of
the smbus_refresh() hack to get around these errors.

Also the vstart settings have been tweaked to work with different
frequency filter settings.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>