i2c: mv64xxx: make the registers offset configurable

The Allwinner i2c controller uses the same logic as the Marvell one, but
with slightly different register offsets.

Introduce a structure that will be passed by either the pdata or
associated to the compatible strings, and that holds the various
registers that might be needed.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Tested-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Tested-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>