ARM: OMAP: Fix map_io for Amstrad E3

Commit 7b88e62f5d219a86d81bdf4388012c97dc42e8f8 (ARM: OMAP1: Use generic
map_io, init_early and init_irq) changed omap1 to use generic map_io.

Looks like I missed one board though. Fix this by adding a custom
map_io for Amstrad E3.

Reported-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Signed-off-by: Tony Lindgren <tony@atomide.com>