ARM: at91: remove at91rm9200_sdramc.h

include/soc/at91/at91rm9200_sdramc.h is replaced by
include/linux/mfd/syscon/atmel-smc.h as this is actually a syscon device.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>