V4L/DVB (4722): Cx88: Add support for VIDIOC_INT_[SR]_REGISTER ioctls

Add support for the advanced debugging ioctls, to allow access to the
cx88 registers from userspace.  Only i2c_id == 0 is supported, for access
to the cx88 adapter itself.  There isn't any support for access to I2C
clients of the adapter.  Most of them don't have R/W registers anyway,
and its necessary to use i2c-dev to talk to them from userspace.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>