V4L/DVB: ngene: split out i2c code into a separate file
Split out the i2c related code from the ngene-core.c into a new file called
ngene-i2c.c. This is part of a larger refactoring of the driver in preparation
for adding analog support.
Note that this patch makes *no* functional change - all I did was cut/paste the
code and add the function prototypes to ngene.h as needed.