drm/exynos: add iommu support for g2d

Chagelog v2:
removed unnecessary structure, struct g2d_gem_node.

Chagelog v1:
This patch adds iommu support for g2d driver. For this, it
adds subdrv_probe/remove callback to enable or disable
g2d iommu. And with this patch, in case of using g2d iommu,
we can get or put device address to a gem handle from user
through exynos_drm_gem_get/put_dma_addr(). Actually, these
functions take a reference to a gem handle so that the gem
object used by g2d dma is released properly.

And runqueue_node has a pointer to drm_file object of current
process to manage gem handles to owner.

This patch is based on the below patch set, "drm/exynos: add
iommu support for -next".
     http://www.spinics.net/lists/dri-devel/msg29041.html

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_gem.c b/drivers/gpu/drm/exynos/exynos_drm_gem.c
index 08d0218..8cb6824 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_gem.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_gem.c
@@ -266,14 +266,14 @@
 	return 0;
 }
 
-void *exynos_drm_gem_get_dma_addr(struct drm_device *dev,
+dma_addr_t *exynos_drm_gem_get_dma_addr(struct drm_device *dev,
 					unsigned int gem_handle,
-					struct drm_file *file_priv)
+					struct drm_file *filp)
 {
 	struct exynos_drm_gem_obj *exynos_gem_obj;
 	struct drm_gem_object *obj;
 
-	obj = drm_gem_object_lookup(dev, file_priv, gem_handle);
+	obj = drm_gem_object_lookup(dev, filp, gem_handle);
 	if (!obj) {
 		DRM_ERROR("failed to lookup gem object.\n");
 		return ERR_PTR(-EINVAL);
@@ -294,12 +294,12 @@
 
 void exynos_drm_gem_put_dma_addr(struct drm_device *dev,
 					unsigned int gem_handle,
-					struct drm_file *file_priv)
+					struct drm_file *filp)
 {
 	struct exynos_drm_gem_obj *exynos_gem_obj;
 	struct drm_gem_object *obj;
 
-	obj = drm_gem_object_lookup(dev, file_priv, gem_handle);
+	obj = drm_gem_object_lookup(dev, filp, gem_handle);
 	if (!obj) {
 		DRM_ERROR("failed to lookup gem object.\n");
 		return;