i2c: Add i2c-icy for I2C on m68k/Amiga

This is the i2c-icy driver for the ICY board for Amiga computers.
It connects a PCF8584 I2C controller to the Zorro bus, providing I2C
connectivity. The original documentation can be found on Aminet:

https://aminet.net/package/docs/hard/icy

IRQ support is currently not implemented, as i2c-algo-pcf is built for
the ISA bus and a straight implementation of the same stack locks up a
Zorro machine.

Signed-off-by: Max Staudt <max@enpas.org>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
[wsa: added a missing newline reported by checkpatch]
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>