drm/exynos: Add plane support with fimd

The exynos fimd supports 5 window overlays. Only one window overlay of
fimd is used by the crtc, so we need plane feature to use the rest
window overlays.

This creates one ioctl exynos specific - DRM_EXYNOS_PLANE_SET_ZPOS, it
is the ioctl to decide for user to assign which window overlay.

Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
diff --git a/drivers/gpu/drm/exynos/exynos_drm_crtc.c b/drivers/gpu/drm/exynos/exynos_drm_crtc.c
index a435c33..e1ce9fd 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_crtc.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_crtc.c
@@ -380,6 +380,7 @@
 
 	exynos_crtc->pipe = nr;
 	exynos_crtc->dpms = DRM_MODE_DPMS_OFF;
+	exynos_crtc->overlay.zpos = DEFAULT_ZPOS;
 	crtc = &exynos_crtc->drm_crtc;
 
 	private->crtc[nr] = crtc;