drm/sun4i: sun4i: Register quirks with the backend structure

In prevision for introducing a new quirk that will be used at atomic
plane check time, register the quirks structure with the backend
structure. This way, it can easily be grabbed where needed.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180719080838.31598-1-paul.kocialkowski@bootlin.com