ARM: pxa: remove pxa93x support

There is currently no devicetree support for pxa930 or pxa935
SoCs, and no board files remain. As it seems unlikely that anyone
is going to add DT support soon, let's drop the SoC specific code
now.

Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>