ARM: dts: add display power domain for exynos5250

The patch adds domain definition and references to it in appropriate devices.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
[mszyprow: rebased onto generic power domains dt bindings]
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Reviewed-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Kukjin Kim <kgene@kernel.org>