qemu: "make check": make number of cores configurable

The QEMU_SMP environment variable or makefile macro may be set to
control the number of cores used during "make check".

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Joakim Bech <joakim.bech@linaro.org>

qemu-check.exp

@@ -42,7 +42,7 @@ info "Starting QEMU..."
 open "serial1.log" "w+"
 spawn -open [open "|tail -f serial1.log"]
 set teecore $spawn_id
-spawn $::env(QEMU) -nographic -monitor none -machine virt -machine secure=on -cpu cortex-a15 -smp 4 -d unimp -semihosting-config enable,target=native -m 1057 -serial stdio -serial file:serial1.log -bios $bios
+spawn $::env(QEMU) -nographic -monitor none -machine virt -machine secure=on -cpu cortex-a15 -smp $::env(QEMU_SMP) -d unimp -semihosting-config enable,target=native -m 1057 -serial stdio -serial file:serial1.log -bios $bios
 expect {
 	"Kernel panic" {
 		info "!!! Kernel panic\n"

qemu.mk

@@ -188,9 +188,11 @@ ifneq ($(TIMEOUT),)
 check-args += --timeout $(TIMEOUT)
 endif
 
+QEMU_SMP ?= 4
 check: $(CHECK_DEPS)
 	cd $(BINARIES_PATH) && \
 		export QEMU=$(ROOT)/qemu/arm-softmmu/qemu-system-arm && \
+		export QEMU_SMP=$(QEMU_SMP) && \
 		expect $(ROOT)/build/qemu-check.exp -- $(check-args) || \
 		(if [ "$(DUMP_LOGS_ON_ERROR)" ]; then \
 			echo "== $$PWD/serial0.log:"; \