sandbox: add a sandbox timer and basic test

Add a sandbox timer which get time from host os and a basic
test.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/test/dm/Makefile b/test/dm/Makefile
index 39630f6..681c6ae 100644
--- a/test/dm/Makefile
+++ b/test/dm/Makefile
@@ -33,5 +33,6 @@
 obj-$(CONFIG_DM_USB) += usb.o
 obj-$(CONFIG_DM_PMIC) += pmic.o
 obj-$(CONFIG_DM_REGULATOR) += regulator.o
+obj-$(CONFIG_TIMER) += timer.o
 obj-$(CONFIG_ADC) += adc.o
 endif