i2c: xiic: Add Xilinx AXI I2C driver

Add Xilinx AXI I2C controller driver based on the Linux i2c-xiic driver.
This driver is stripped of all the IRQ handling and uses pure polling,
yet tries to retain most of the structure of the Linux driver to make
backporting of fixes easy.

Note that the IP has a known limitation on 255 bytes read and write,
according to xilinx this is still being worked on [1].

[1] https://forums.xilinx.com/t5/Embedded-Processor-System-Design/AXI-IIC-V2-0-I2C-Master-Reading-multiple-bytes-from-I2C-slave/m-p/854419/highlight/true#M39387



Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Heiko Schocher <hs@denx.de>
Reviewed-by: Heiko Schocher <hs@denx.de>