ARM: pxa3xx: add generic DT machine code

Add a DT_MACHINE_START entry for PXA3xx machines and a auxdata table for
some of the devices. This file can be extended to also support pxa2xx
and pxa9xx boards.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Haojian Zhuang <haojian.zhuang@gmail.com>