ARM: iop32x: enable multiplatform support

After iop32x was converted to the generic multi-irq entry
code, nothing really stops us from building it into a
generic kernel.

The two last headers can simply be removed, the mach/irqs.h
gets replaced with the sparse-irq intiialization from the
board specific .nr_irqs value, and the decompressor debug
output can use the debug_ll hack that all other platforms
use.

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