ARM: dts: update display related nodes for exynos5250-snow

Add DT nodes for ptn3460 bridge chip and panel.
Add backlight enable pin and backlight power supply for pwm-backlight.
Also add bridge phandle needed by dp to enable display on snow.

Signed-off-by: Ajay Kumar <ajaykumar.rs@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>