irqchip/gic-v3: Fix translation of LPIs after conversion to irq_fwspec

Commit f833f57f ("irqchip: Convert all alloc/xlate users from
of_node to fwnode") converted the GICv3 driver to using irq_fwspec
as part of its 'translate' method.

Too bad it ended up with a copy of the GICv2 'translate' method,
which screws up LPI translation (by not translating them at all).

Restore the code in its original shape, and just change what is
really required...

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: <linux-arm-kernel@lists.infradead.org>
Cc: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
Cc: Duc Dang <dhdang@apm.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Link: http://lkml.kernel.org/r/1444822037-16983-2-git-send-email-marc.zyngier@arm.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>