ARM i.MX53: Add GPU clocks to clock tree

ARM i.MX53: Add GPU clocks to clock tree

This patch adds the missing GPU2D and GPU3D mux and gate clocks,
and the graphics arbiter gate clock.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>