drm/exynos: add render node support

This patch allows clients who want to use render node to access
rendering relevant ioctls - g2d, post processor and gem allocation.

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

diff --cc drivers/gpu/drm/exynos/exynos_drm_drv.c
Simple merge