irqchip: move IRQ driver for Armada 370/XP

irqchip: move IRQ driver for Armada 370/XP

When the Marvell Armada 370/XP support was included in the kernel, the
drivers/irqchip/ directory didn't exist and the minimal infrastructure
in it also didn't exist. Now that we have those things in place, we
move the Armada 370/XP IRQ controller driver from
arch/arm/mach-mvebu/irq-armada-370-xp.c to
drivers/irqchip/irq-armada-370-xp.c.

Note in order to reduce code movement and therefore ease the review of
this patch, we intentionally introduce a forward declaration of
armada_370_xp_handle_irq(). It is in fact not needed because this
handler can now simply be implemented before
armada_370_xp_mpic_of_init(). That will be done in the next commit.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>