xen/arm: Add support for GICv3 for domU

xen/arm: Add support for GICv3 for domU

The vGIC will emulate the same version as the hardware. The toolstack has
to retrieve the version of the vGIC in order to be able to create the
corresponding device tree node.

A new DOMCTL has been introduced for ARM to configure the domain. For now
it only allow the toolstack to retrieve the version of vGIC.
This DOMCTL will be extend later to let the user choose the version of the
emulated GIC.

Signed-off-by: Vijaya Kumar K <Vijaya.Kumar@caviumnetworks.com>
Signed-off-by: Julien Grall <julien.grall@linaro.org>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Jan Beulich <jbeulich@suse.com>
Acked-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Cc: Wei Liu <wei.liu2@citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>