log: Add a test command

Add a command which exercises the logging system.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/Makefile b/test/Makefile
index 6305afb..40f2244 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -10,3 +10,4 @@
 obj-$(CONFIG_SANDBOX) += compression.o
 obj-$(CONFIG_SANDBOX) += print_ut.o
 obj-$(CONFIG_UT_TIME) += time_ut.o
+obj-$(CONFIG_$(SPL_)LOG) += log/