OMAP3: Fix CKE1 MUX setting to allow self-refresh

The Beagle rev Cx and Overo boards are using both SDRC CSes. The MUX
setting is needed for the second CS clock signal to allow the 2 RAM
parts to be put in self-refresh correctly. This also works on rev B
Beagle boards with 128M of RAM.

From: Steve Sakoman <steve@sakoman.com>
From: Jean Pihet <jpihet@mvista.com>
Signed-off-by: Jean Pihet <jpihet@mvista.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Dirk Behme <dirk.behme@googlemail.com>