ARM: sa1111: provide a generic way to prevent devices from registering

Some platforms don't want certain devices to be registered, because,
eg, the interface is not wired.  Provide a way for platforms to
prevent various devices from being registered via a devid bitmask in
the platform data.

Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>