drm/<drivers>: Unified handling of unimplemented fb->create_handle

Some drivers don't have real ->create_handle callbacks.

- cirrus/ast/mga200: Returns either 0 or -EINVAL.

- udl: Didn't even bother with a callback, leading to a nice
  userspace-triggerable OOPS.

- vmwgfx: This driver bothered with an implementation to return 0 as
  the handle (which is the canonical no-obj gem handle).

All have in common that ->create_handle doesn't really make too much
sense for them - that ioctl is used only for seamless fb takeover in
the radeon/nouveau/i915 ddx drivers. So allow drivers to not implement
this and return a consistent -ENODEV.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/ast/ast_main.c

@@ -246,16 +246,8 @@ static void ast_user_framebuffer_destroy(struct drm_framebuffer *fb)
 	kfree(fb);
 }
 
-static int ast_user_framebuffer_create_handle(struct drm_framebuffer *fb,
-					      struct drm_file *file,
-					      unsigned int *handle)
-{
-	return -EINVAL;
-}
-
 static const struct drm_framebuffer_funcs ast_fb_funcs = {
 	.destroy = ast_user_framebuffer_destroy,
-	.create_handle = ast_user_framebuffer_create_handle,
 };