ARM: at91: add ram controller DT support

We can now drop the call to ioremap_registers() as we have the binding for the
SDRAM/DDR Controller.

Drop ioremap_registers() for sam9x5 too.

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>