ARM: cns3xxx: initial DT support

This adds very minimal support for booting cns3xxx using a device
tree. It should support the same devices that cns3420vb provides
but gets them from the DT. All devices that don't have their own
binding are probed through auxdata. This is completely untested
and likely incomplete.

Booting through ATAGS is made optional, so it can be turned off
by anybody who has a DTB file.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>