[media] ddbridge: add I2C functions, add XO2 module support

Some Flex modules (mostly with anyof C/C2/T/T2 demods based on the Sony
CXD28xxER series) are equipped with an interface named XO2 (which
appears to be the Lattice MachXO2). Add functionality to detect such
links and initialise them, so any tuner module with such an interface can
be used.

This also adds dummy detection for any possible connected module, telling
the user it isn't supported at this very moment.

Also adds i2c_io(), i2c_write() and i2c_write_reg(), all required for the
XO2 handling functionality.

Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>