drm: Assert that BO is locked in drm_gem_vram_{pin, unpin}_locked()

We may not call drm_gem_vram_{pin,unpin}_locked() with an unlocked
BO. Now test for this.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20190521110831.20200-4-tzimmermann@suse.de


Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>