xen: arm: add a quirk to handle platforms with unusual GIC layout

xen: arm: add a quirk to handle platforms with unusual GIC layout

On some platforms the pages are placed at a 64K stride instead of as
contiguous 4K pages.

This is because the ARM64 architecture allows for page sizes of 4/16/64K in
the MMU so a larger stride allow more granular control of mappings. We only
currently support 4K.

Use this quirk on the xgene platform.

This should ideally be fixed by an extension to the device tree bindings as
described in http://www.spinics.net/lists/devicetree/msg10473.html especially
http://www.spinics.net/lists/devicetree/msg10478.html. However for the time
being a platform specific quirk will do.

Note that we always map the GICV to the guest (including dom0) at a 4K stride
length and this is reflected in the DTB passed to the guest.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Acked-by: Julien Grall <julien.grall@linaro.org>