i2c: Add driver for Cadence I2C controller

Add a driver for the Cadence I2C controller. This controller is for
example found in Xilinx Zynq.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Tested-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Harini Katakam <harinik@xilinx.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

diff --cc MAINTAINERS
Simple merge

diff --cc drivers/i2c/busses/Kconfig
Simple merge

diff --cc drivers/i2c/busses/Makefile
Simple merge

diff --cc drivers/i2c/busses/i2c-cadence.c
Simple merge