ARM: OMAP5: Clean up iosettings code

There is some code duplication in the ddr io settings code.
This is avoided by moving the data to a Soc specific place and
letting the code generic.

This avoids unnessecary code addition for future socs.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@ti.com>