ARM: picoxcell: remove .nr_irqs reference

A recent cleanup caused build errors in some configurations
because the header defining NR_IRQS_LEGACY is not included
here. Since that value is the default, we can just as well
leave it out.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Jamie Iles <jamie@jamieiles.com>