arm: mvebu: turris_omnia: move I2C dependencies to Kconfig

arm: mvebu: turris_omnia: move I2C dependencies to Kconfig

The I2C dependencies are defined in include/configs/turris_omnia.h,
because Turris Omnia won't boot correctly without I2C support.

Move these dependencies to Kconfig, so that they are selected if Turris
Omnia is selected as target.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Stefan Roese <sr@denx.de>