[ARM] generic: Add DTS files for booting Xvisor ARM32 on VExpress-A15

For debugging purpose we might need to boot Xvisor ARM32 (without
virtualization extension) on VExpress-A15 emulated by ARM Fast Models
hence this patch adds required DTS files.

Other than debugging, there is no real use-case is using Xvisor ARM32
on HW having virtualization extensions. We should always use Xvisor ARM32ve
for HW having virtualization extensions.

Signed-off-by: Anup Patel <anup@brainfault.org>