drm/exynos: cleanup for hdmi platform data

The exynos_drm_hdmi_pdata struct have owned unnessary members. Remove
them and add a function pointer to configure hdmi hotplug detection pin.

Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>