media: i2c: ak7375: Prepare for supporting another chip

In view of adding support for at least one other chip,
change the driver to move chip-specific properties and
values in a common structure.

No functional changes.

Signed-off-by: Vincent Knecht <vincent.knecht@mailoo.org>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>