irqchip/gic-v4: Add some basic documentation

Do a braindump of the way things are supposed to work.

Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
1 file changed