armv8r64-extras/xen: Fix zephyr-philosophers booting failure

When zephyr-philosophers is running on Xen, it fails at the assertion
to check whether GICD_CTRL_NS is 1. The reason for the failure is:

    On Armv8R-64, all of stuff are running in secure state and there is
    no non-secure world. The GIC implementation supports only single
    security state. But VGICD_CTLR_DEFAULT is non-secure state in
    current Xen implementation.

This downstream patch set VGICD_CTLR_DEFAULT as
GICD_CTLR_DS|GICD_CTLR_ARE to avoid the issues like above.

Issue-Id: SCM-5560
Signed-off-by: Jiacheng Tang <jiacheng.tang@arm.com>
Change-Id: I4ddfc5dff786ac07a77c4e56746d969ac509d741
Signed-off-by: Robbie Cao <robbie.cao@arm.com>