ARM: dts: move dp hpd gpio pin to pinctrl_0 for exynos5420 peach_pit

DP Hpd Gpio pin which is "gpx2-6" in Exynos 5420 based peach board,
belongs to Pinctrl_0. It has moved to pinctrl_0 from pinctrl_3.

Signed-off-by: Rahul Sharma <rahul.sharma@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>