dts: exynos5422: make clear what's needed to enable displayport

Change-Id: I703daef593936c5d4e4c13454c18ad5313c1b743
ARM: dts: exynos5422: instead of commenting lets just leave it disabled

Change-Id: I3d4f6a84d52da974d9222b8e64ff2c06ad5bcae4