ARM: pxa: pxa27x skip default device initialization with DT

When booting via DT, the default PXA devices must not have been probed
before, otherwise the augmented information from the device tree is
ignored.

This is the twin commit of commit 82ce44d1 ("ARM: pxa3xx: skip
default device initialization when booting via DT").

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Acked-by: Daniel Mack <daniel@zonque.org>