samsung: exynos: Convert SROMC interface to a driver

Add a bus driver for this and use it to configure the bus parameters for
the Ethernet interface. Drop the old pre-driver-model code.

Switch over to use driver model for Ethernet.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>