ARM: 6606/1: sa1100: Fix platform device registration

Since commit 7a5b4e16, simpad devices don't
boot anymore, since platform devices are registered too early. Fix by moving
the registration from map_io to arch_initcall as done on other sa1100 boards.

Signed-off-by: Jochen Friedrich <jochen@scram.de>
Acked-by: Kristoffer Ericson <kristoffer.ericson@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>