i2c: keba: Add KEBA I2C controller support

The KEBA I2C controller is found in the system FPGA of KEBA PLC devices.
It is used to connect EEPROMs and hardware monitoring chips. The

It is a simple I2C controller with a fixed bus speed of 100 kbit/s. The
whole message transmission is executed by the driver. The driver
triggers all steps over control, status and data register. There are no
FIFOs or interrupts.

Signed-off-by: Gerhard Engleder <eg@keba.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>