scons: change ARM default protocol to CHI

Change-Id: Ic05f96b84a4e61e93bc12e48381c6a809f260021
Signed-off-by: Tiago Mück <tiago.muck@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/42564
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
diff --git a/build_opts/ARM b/build_opts/ARM
index c473078..e4cb9a5 100644
--- a/build_opts/ARM
+++ b/build_opts/ARM
@@ -1,3 +1,3 @@
 TARGET_ISA = 'arm'
 CPU_MODELS = 'AtomicSimpleCPU,TimingSimpleCPU,O3CPU,MinorCPU'
-PROTOCOL = 'MOESI_CMP_directory'
+PROTOCOL = 'CHI'