drm/exynos: Replace repeated declaration by include <drm/drmP.h>

Re-declare struct is not a good practice, let's use the original
drm declarations.
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos_drm_drv.h

@@ -15,6 +15,7 @@
 #ifndef _EXYNOS_DRM_DRV_H_
 #define _EXYNOS_DRM_DRV_H_
 
+#include <drm/drmP.h>
 #include <linux/module.h>
 
 #define MAX_CRTC	3
@@ -36,9 +37,6 @@
 
 #define wait_for(COND, MS) _wait_for(COND, MS)
 
-struct drm_device;
-struct drm_connector;
-
 /* This enumerates device type. */
 enum exynos_drm_device_type {
 	EXYNOS_DEVICE_TYPE_NONE,