misc: keba: Add fan device

Add support for the fan auxiliary device. This enables monitoring of the
fan.

Signed-off-by: Gerhard Engleder <eg@keba.com>
Link: https://lore.kernel.org/r/20241011191257.19702-7-gerhard@engleder-embedded.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>