tools/libxl: arm: Use an higher value for the GIC phandle

tools/libxl: arm: Use an higher value for the GIC phandle

The partial device tree may contains phandle. The Device Tree Compiler
tends to allocate the phandle from 1.

Reserve the ID 65000 for the GIC phandle. I think we can safely assume
that the partial device tree will never contain a such ID.

Signed-off-by: Julien Grall <julien.grall@linaro.org>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Cc: Ian Jackson <ian.jackson@eu.citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>