ARM: pxa: move declarations to proper place

Platform data is not the right place for such declarations, use
devices.h in the mach-directory where the rest is located. Note that the
some board files needed an additional include for this to work.

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>