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>

docs/man/xl.cfg.pod.5

@@ -470,6 +470,9 @@ the user to defined aliases which can be used by the guest kernel.
 Given the complexity of verifying the validity of a device tree, this
 option should only be used with trusted device tree.
 
+Note that the partial device tree should avoid to use the phandle 65000
+which is reserved by the toolstack.
+
 =back
 
 =head2 Devices

tools/libxl/libxl_arm.c

@@ -81,10 +81,11 @@ static struct arch_info {
     {"xen-3.0-aarch64", "arm,armv8-timer", "arm,armv8" },
 };
 
-enum {
-    PHANDLE_NONE = 0,
-    PHANDLE_GIC,
-};
+/*
+ * The device tree compiler (DTC) is allocating the phandle from 1 to
+ * onwards. Reserve a high value for the GIC phandle.
+ */
+#define PHANDLE_GIC (65000)
 
 typedef uint32_t be32;
 typedef be32 gic_interrupt[3];

tools/libxl/libxl_types.idl

@@ -416,6 +416,8 @@ libxl_domain_build_info = Struct("domain_build_info",[
     # Given the complexity of verifying the validity of a device tree,
     # libxl doesn't do any security check on it. It's the responsibility
     # of the caller to provide only trusted device tree.
+    # Note that the partial device tree should avoid to use the phandle
+    # 65000 which is reserved by the toolstack.
     ("device_tree",      string),
     ("u", KeyedUnion(None, libxl_domain_type, "type",
                 [("hvm", Struct(None, [("firmware",         string),