ARM: at91: move at91rm9200 sdramc defines to at91rm9200_sdramc.h

This cleanup is done to allow to have multiple SoC in the same image.

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