xen/arm: gicv2: Export GICv2m register frames to Dom0 by device tree

xen/arm: gicv2: Export GICv2m register frames to Dom0 by device tree

This patch adds v2m extension support in GIC-v2 driver. The GICv2 driver
detects the MSI frames from device tree and creates corresponding device
tree nodes in dom0's DTB. It also provides one hw_ops callback to map
v2m MMIO regions to dom0 and route v2m SPIs to dom0.

With this GICv2m extension support, the dom0 kernel can do GICv2m frame
setup and initialization.

This patch is based on the GICv2m patch of Suravee Suthikulpanit:
[PATCH 2/2] xen/arm: gicv2: Adding support for GICv2m in Dom0
http://lists.xen.org/archives/html/xen-devel/2015-04/msg02613.html

Signed-off-by: Wei Chen <Wei.Chen@linaro.org>
Reviewed-by: Julien Grall <julien.grall@arm.com>