V4L/DVB (12417): I2C cleanups and version checks

The structure and comments of the I2C part have been adopted to fit to the
USB part.

Some additional cleanups and precisements have been made to the version
detection and checking functionality to clearly separate HW/SW/FW version.

Signed-off-by: Tobias Lorenz <tobias.lorenz@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>