drm/exynos: added ipp device registration to drm driver

This patch added exynos-drm-ipp platform device registration to the exynos drm
driver. When DT is enabled, platform devices need to be registered within the
driver code. This patch fits the requirement of both DT and Non DT based drm
drivers.

Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Signed-off-by: Donghwa Lee <dh09.lee@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>