ARM: pxa: remove irq init from dt machines

The init_irq and handle_irq can be declared through standard irqchip
declaration and are not necessary in machine descriptions.

This is another step towards the generic kernel for the pxa
architecture.

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