ARM i.MX5: switch IPU clk support to devicetree bindings

The i.MX5 clk support has platform based clock bindings for the
IPU. IPU support is devicetree only, so move them over to devicetree
based bindings. Also, enable MIPI clocks which do not have a device
associated with, but still need to be enabled to do graphics on
i.MX51.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Shawn Guo <shawn.guo@linaro.org>