misc: keba: Add SPI controller device

Add support for the SPI controller auxiliary device. This enables access
to the SPI flash of the FPGA and some other SPI devices.

The actual list of SPI devices is detected by reading some bits out of
the previously registered I2C EEPROM.

Signed-off-by: Gerhard Engleder <eg@keba.com>
Link: https://lore.kernel.org/r/20241011191257.19702-4-gerhard@engleder-embedded.com


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