qemu: Add '-machine secure=on' to arguments

This is required to move OP-TEE to upstream QEMU.

Signed-off-by: Victor Chong <victor.chong@linaro.org>
Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Tested-by: Victor Chong <victor.chong@linaro.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Reviewed-by: Joakim Bech <joakim.bech@linaro.org>
diff --git a/qemu.mk b/qemu.mk
index 5bdc0c2..f20194d 100644
--- a/qemu.mk
+++ b/qemu.mk
@@ -214,7 +214,7 @@
 	$(QEMU_PATH)/arm-softmmu/qemu-system-arm \
 		-nographic \
 		-serial tcp:localhost:54320 -serial tcp:localhost:54321 \
-		-s -S -machine virt -cpu cortex-a15 \
+		-s -S -machine virt -machine secure=on -cpu cortex-a15 \
 		-m 1057 \
 		-bios $(ROOT)/out/bios-qemu/bios.bin $(QEMU_EXTRA_ARGS)