ARM i.MX51: setup MIPI during startup

The MIPI interface has to be initialized for proper IPU support.
The MIPI officially is not supported, but still needs initialization.
This patch adds this to the SoC startup as all it does is poking
some magic values into registers for which we do not have documentation.

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