[ARM] generic: Don't include VExpress-A15 guest template in vexpress-a15-nove.dtsi

We don't have generic timers and VGIC for Xvisor ARM32 running on VExpress-A15
host hence we cannot prove VExpress-A15 guest on Xvisor ARM32.

For VExpress-A15 guest we will have to used Xvisor ARM32ve or Xvisor ARM64.

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