Detect and initialise modules equipped with XO2 interfaces (Lattice
MachXO2). This requires a few more I2C transfer functions which this adds
as well. Defines for the different possible (available) module types are
added to ngene.h. The support for the actual tuners contained on these
addon modules is kept separate from this commit and is being added with
the next commits.

The xo2names array is temporarily marked __maybe_unused to silence a
corresponding compiler warning at this stage.
Signed-off-by: Daniel Scheller <d.scheller@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>