dm: exynos: Split out the cros_ec drivers

dm: exynos: Split out the cros_ec drivers

With the driver model conversion we are going to be using driver model for
SPI and not for I2C. This works OK so long as a board doesn't need both
dm and non-dm versions of the cros_ec driver. Since pit uses SPI and snow
uses I2C we need to split the configs so that only one driver is compiled
for each platform.

We can fix this later when driver model supports I2C.

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