ARM: dts: fix mmc node updates for exynos5250-spring

Resolve a merge conflict with mmc refactoring aaa25a5a ("ARM: dts:
unuse the slot-node and deprecate the supports-highspeed for dw-mmc in
exynos") by dropping the slot@0 nodes, moving its bus-width property to
the mmc node and replacing supports-highspeed with cap-{mmc,sd}-highspeed,
matching exynos5250-snow.

Cc: Jaehoon Chung <jh80.chung@samsung.com>
Fixes: 53dd4138

 ("ARM: dts: Add exynos5250-spring device tree")
Signed-off-by: Andreas Faerber <afaerber@suse.de>
Reviewed-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Cc: <stable@vger.kernel.org>        [3.19+]
Signed-off-by: Kukjin Kim <kgene@kernel.org>