ARM: dts: ixp4xx: Group PCI interrupt properties together

Move the PCI 'interrupt-map-mask' and '#interrupt-cells' properties
alongside the 'interrupt-map' property in each board dts. This avoids
having incomplete set of interrupt properties which may fail validation.

Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Rob Herring <robh@kernel.org>