drm/vma: Add a driver_private member to vma_node.

This allows drivers to distinguish between different types of vma_node's.
The readonly flag was unused and is thus removed.

This is a temporary solution, until i915 is converted completely to
use ttm for bo's.

Signed-off-by: Maarten Lankhorst <[e-mail]>
Reviewed-by: Thomas Hellström <[e-mail]>
Acked-by: Daniel Vetter <[e-mail]> #irc
Signed-off-by: Maarten Lankhorst <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_gem.c

···
 		return -EACCES;
 	}
 
-	if (node->readonly) {
-		if (vma->vm_flags & VM_WRITE) {
-			drm_gem_object_put(obj);
-			return -EINVAL;
-		}
-
-		vma->vm_flags &= ~VM_MAYWRITE;
-	}
-
 	ret = drm_gem_mmap_obj(obj, drm_vma_node_size(node) << PAGE_SHIFT,
 			       vma);
 

include/drm/drm_vma_manager.h

···
 	rwlock_t vm_lock;
 	struct drm_mm_node vm_node;
 	struct rb_root vm_files;
-	bool readonly:1;
+	void *driver_private;
 };
 
 struct drm_vma_offset_manager {