drm/exynos: Move display implementation into dp

This patch moves the exynos_drm_display implementation from fimd into
the dp driver. This will allow for tighter integration of the dp driver
into the exynos drm driver.

Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Inki Dae <inki.dae@samsung.com>