OMAP3: Setup MUX settings for SDRC CKE signals

This patches ensures the MUX settings are correct for the SDRC
CKE signals to SDRAM. This allows the self-refresh to work when
2 chip-selects are in use.

A warning is thrown away in case the initial muxing is incorrect,
in order to track faulty or old-dated bootloaders.
Note: The CONFIG_OMAP_MUX and CONFIG_OMAP_MUX_WARNINGS options
must be enabled for the mux code to have effect.

Signed-off-by: Jean Pihet <jpihet@mvista.com>
Signed-off-by: Paul Walmsley <paul@pwsan.com>