ARM: dts: Fold exynos5250-cros-common into exynos5250-snow

exynos5250-cros-common.dtsi was meant for sharing common pieces across
ChromeOS devices. This turned out premature, as several devices ended up
in the common file that are not common after all. Since the remaining
common ChromeOS pieces are fairly minor,  exynos5250-cros-common.dtsi
was requested to be merged into the Snow device tree, sharing only the
keyboard controller for now. This may be re-evaluated as both mature.

Suggested-by: Doug Anderson <dianders@chromium.org>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Andreas Faerber <afaerber@suse.de>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>