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/drivers/timer/Makefile b/drivers/timer/Makefile
index ae66c07..300946e 100644
--- a/drivers/timer/Makefile
+++ b/drivers/timer/Makefile
@@ -6,3 +6,4 @@
 
 obj-$(CONFIG_TIMER)		+= timer-uclass.o
 obj-$(CONFIG_ALTERA_TIMER)	+= altera_timer.o
+obj-$(CONFIG_SANDBOX_TIMER)	+= sandbox_timer.o