CONFIG: SMDK5250: I2C: Enable I2C

This enables I2C support on smdk5250.
Pinmux setting moved to board file to avoid repeated setting of
gpio lines.

Signed-off-by: Alim Akhtar <alim.akhtar@samsung.com>
Signed-off-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Rajeshwari Shinde <rajeshwari.s@samsung.com>
Acked-by: Simon Glass <sjg@chromium.org>