i2c: add support for offset overflow in to address

Some devices (2 wire eeproms for example) use some bits from the chip
address to represent the high bits of the offset instead of or as well
as using multiple bytes for the offset, effectively stealing chip
addresses on the bus.

Add a chip offset mask that can be set for any i2c chip which gets
filled with the offset overflow during offset setup.

Signed-off-by: Robert Beckett <bob.beckett@collabora.com>
Signed-off-by: Ian Ray <ian.ray@ge.com>
Reviewed-by: Heiko Schocher <hs@denx.de>