irqchip: sun4i: Fix irq 0 not working

SUN4I_IRQ_VECTOR_REG containing 0 can mean one of 3 things:
1) no more irqs pending
2) irq 0 pending
3) spurious irq

So if we immediately get a reading of 0, check the irq-pending reg
to differentiate between 2 and 3. We only do this once to avoid
the extra check in the common case of 1) hapening after having
read the vector-reg once.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
irqchip: sun4i: Fix a comment about mask register initialization

The comment was claiming that we were masking all irqs, while the code actually
*un*masks all of them.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
ARM: sun4i: dt: Add axp209 support to various boards

Signed-off-by: Hans de Goede <hdegoede@redhat.com>