drm/cirrus: Move to drm/tiny

Because it is. Huge congrats to everyone who made this kind of
refactoring happen!

Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Dave Airlie <airlied@redhat.com>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: virtualization@lists.linux-foundation.org
Link: https://patchwork.freedesktop.org/patch/msgid/20200415074034.175360-38-daniel.vetter@ffwll.ch