drm: add mmap function to prime helpers

This adds to call low-level mmap() from prime helpers.

Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 82670ac..12083dc 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -937,6 +937,8 @@
 				struct sg_table *sgt);
 	void *(*gem_prime_vmap)(struct drm_gem_object *obj);
 	void (*gem_prime_vunmap)(struct drm_gem_object *obj, void *vaddr);
+	int (*gem_prime_mmap)(struct drm_gem_object *obj,
+				struct vm_area_struct *vma);
 
 	/* vga arb irq handler */
 	void (*vgaarb_irq)(struct drm_device *dev, bool state);