irqchip/gicv3-its: Add HW revision detection and configuration

Some GIC revisions require an individual configuration to esp. add
workarounds for HW bugs. This patch implements generic code to parse
the hw revision provided by an IIDR register value and runs specific
code if hw matches. A function is added that reads the IIDR registers
for ITS (GITS_IIDR) and then goes through a list of init functions to
be called for specific versions. Same could be done for GICV3
(GICD_IIDR), but there are no users yet for it.

The patch is needed to implement workarounds for HW errata in Cavium's
ThunderX GICV3 ITS.

Signed-off-by: Robert Richter <rrichter@cavium.com>
Reviewed-by: Marc Zygnier <marc.zyngier@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Cc: Tirumalesh Chalamarla <tchalamarla@cavium.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Jason Cooper <jason@lakedaemon.net>
Link: http://lkml.kernel.org/r/1442869119-1814-5-git-send-email-rric@kernel.org


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