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/Kconfig b/drivers/timer/Kconfig
index 97c4128..601e493 100644
--- a/drivers/timer/Kconfig
+++ b/drivers/timer/Kconfig
@@ -16,4 +16,11 @@
 	  Select this to enable an timer for Altera devices. Please find
 	  details on the "Embedded Peripherals IP User Guide" of Altera.
 
+config SANDBOX_TIMER
+	bool "Sandbox Timer support"
+	depends on SANDBOX && TIMER
+	help
+	  Select this to enable an emulated timer for sandbox. It gets
+	  time from host os.
+
 endmenu