Only increase SMP for CrosVM HelloWorld tests

We increased number of QEMU-emulated CPUs from 2 to 4 to increase
chances of discovering concurrency issues but since Make runs `nproc`
jobs simultaneously, the system starts thrashing.

Reduce number of CPUs back down to 2 by default but keep 4 for CrosVM
HelloWorld tests. This covers boot and spawning a guest VM, at least.

Change-Id: Id45dd87ab94e6df4003443ea7f874157297f3779
diff --git a/Makefile b/Makefile
index 51f51db..dd03eab 100644
--- a/Makefile
+++ b/Makefile
@@ -448,6 +448,7 @@
 		-F $(UBOOT_BIN) \
 		-o $(CROSVM_HELLOWORLD_LOG_DIR)/$(1).log \
 		$(CROSVM_HELLOWORLD_SCRIPT_DIR)/host.sh -- \
+		-s 4 \
 		-R $(CROSVM_HELLOWORLD_SCRIPT_DIR)/guest.sh \
 		-R $(KERNEL_IMAGE) \
 		-R $(PREBUILTS_ROOTFS_EXT4) \
diff --git a/aarch64/run_qemu.sh b/aarch64/run_qemu.sh
index 2aa338f..95e0798 100755
--- a/aarch64/run_qemu.sh
+++ b/aarch64/run_qemu.sh
@@ -22,7 +22,7 @@
 default_var ROOTFS		"${PREBUILTS_KUT_ROOTFS}"
 default_var FIRMWARE		""
 default_var CPU			""
-default_var SMP			4
+default_var SMP			2
 default_var RAM			512
 default_var GIC			3
 default_var GDB			0