i2c:soft:multi: Support for multiple soft I2C buses at Samsung boards

Support for multiple soft I2C buses.

Multibus I2C support is achieved by defining get_multi_{sda|scl}_pin
functions to switch between multiple "soft" I2C buses.

Common definition of I2C_X I2C buses is provided at <i2c.h>.

TEST HW:
     Samsung's Exynos4210 evt.0.1 - Trats development board

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Heiko Schocher <hs@denx.de>
Cc: Minkyu Kang <mk7.kang@samsung.com>
Acked-by: Heiko Schocher <hs@denx.de>