ARM: dts: Update video-phy node with syscon phandle for exynos3250

As a follow-up to recent changes to Exynos mipi video phy driver,
introducing support for PMU regmap in commit e4b3d380 ("phy:
exynos-video-mipi: Fix regression by adding support for PMU regmap")
add a syscon phandle to video-phy node to bring back to life both
MIPI DSI display and MIPI CSIS-2 camera sensor on Exynos3250.

Signed-off-by: Beata Michalska <b.michalska@samsung.com>
Reviewed-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Kukjin Kim <kgene@kernel.org>