ARM: pxa: convert to multiplatform

PXA is now ready to be built into a single kernel with all the
other ARMv5 platforms, so change the Kconfig bit to finish it
off. The mach/uncompress.h support is the last bit that goes away,
getting replaced with the normal DEBUG_LL based approach.

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