irqchip: gic: Add an entry point to set up irqchip flags

A common use of gic_arch_extn is to set up additional flags
to the GIC irqchip. It looks like a benign enough hack that
doesn't really require the users of that feature to be converted
to stacked domains.

Add a gic_set_irqchip_flags() function that platform code can
call instead of using the dreaded gic_arch_extn.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Link: https://lkml.kernel.org/r/1426088737-15817-2-git-send-email-marc.zyngier@arm.com


Signed-off-by: Jason Cooper <jason@lakedaemon.net>