[ARM] 4755/1: [AT91] NAND update

Map the complete memory region (SZ_256M) as is done on the other AT91
processors.

The SMC_SMARTMEDIA bit should be set in the EBI controller to enable
the hardware NAND logic.
  (Patch from Sascha Erlacher)

Signed-off-by: Andrew Victor <linux@maxim.org.za>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>