configs: fix fastmodel configs to run with kernel 5.x

The original config can't run under kernel 5.x. Since atomic operation
on fastmodel doesn't work well, I decide to disable related configs
(BROADCASTATOMIC and BROADCASTOUTER) to unblock the boot process.

Change-Id: Ibe622e22ee918446ae4f5a4b7fc8bcacd280ba6f
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/62211
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Yu-hsin Wang <yuhsingw@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>

configs/example/arm/devices.py

@@ -268,7 +268,9 @@ class FastmodelCluster(SubSystem):
         ]
         CpuClass = CpuClasses[num_cpus - 1]
 
-        cpu = CpuClass(GICDISABLE=False)
+        cpu = CpuClass(
+            GICDISABLE=False, BROADCASTATOMIC=False, BROADCASTOUTER=False
+        )
         for core in cpu.cores:
             core.semihosting_enable = False
             core.RVBARADDR = 0x10