test: Keep track of suite duration

Show the time taken by each test suite with 'ut all' and the total time
for all suites.

Take care to remove any sandbox time-offset from the values.

Fix the comment-format on timer_test_add_offset() while we are here.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/timer/sandbox_timer.c b/drivers/timer/sandbox_timer.c
index e8b54a0..c1baf3c 100644
--- a/drivers/timer/sandbox_timer.c
+++ b/drivers/timer/sandbox_timer.c
@@ -18,6 +18,11 @@
 	sandbox_timer_offset += offset;
 }
 
+ulong timer_test_get_offset(void)
+{
+	return sandbox_timer_offset;
+};
+
 u64 notrace timer_early_get_count(void)
 {
 	return os_get_nsec() / 1000 + sandbox_timer_offset * 1000;