xen: arm: X-Gene Storm check GIC DIST address for EOI quirk

xen: arm: X-Gene Storm check GIC DIST address for EOI quirk

In old X-Gene Storm firmware and DT, secure mode addresses have been
mentioned in GICv2 node. In this case maintenance interrupt is used
instead of EOI HW method.

This patch checks the GIC Distributor Base Address to enable EOI quirk
for old firmware.

Ref:
http://lists.xen.org/archives/html/xen-devel/2014-07/msg01263.html

Signed-off-by: Pranavkumar Sawargaonkar <pranavkumar@linaro.org>
Tested-by: Christoffer Dall <christoffer.dall@linaro.org>
Reviewed-by: Julien Grall <julien.grall@citrix.com>
Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>