smptest: Don't wait 15 seconds for every inactive cpu

Our current qemu builds have 28 inactive cpus. The delay here added 14
minutes to the all the pre-submit and post-submit builds that run this
test twice.

Bug: None
Change-Id: Iad4ba405cfe9f75141b617c110ce2e1f8dc20b22

app/smptest/smptest.c

diff --git a/app/smptest/smptest.c b/app/smptest/smptest.c
index 7ea3fee..6551df9 100644
--- a/app/smptest/smptest.c
+++ b/app/smptest/smptest.c
@@ -178,7 +178,8 @@
              * (up to 1 sec, then think they got stuck).
              */
             for (int i = 0; i < 10; i++) {
-                if (smpt->unblock_count != j || smpt->done_count != j) {
+                if (smpt->started &&
+                    (smpt->unblock_count != j || smpt->done_count != j)) {
                     thread_sleep(100);
                 }
             }