media: dt-bindings: ak7375: Add ak7345 support

Document AK7345 bindings. Compared to AK7375, it has only 9 bits position
values (instead of 12), 20 ms power-up delay (instead of 10), and no known
standby register setting.

Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Vincent Knecht <vincent.knecht@mailoo.org>
[Sakari Ailus: Rewrap commit message.]
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>