test: Add gpio-sysinfo test

This adds a test for the gpio-sysinfo driver.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/sandbox_flattree_defconfig b/configs/sandbox_flattree_defconfig
index 97ac46d..853c944 100644
--- a/configs/sandbox_flattree_defconfig
+++ b/configs/sandbox_flattree_defconfig
@@ -178,6 +178,7 @@
 CONFIG_SPMI_SANDBOX=y
 CONFIG_SYSINFO=y
 CONFIG_SYSINFO_SANDBOX=y
+CONFIG_SYSINFO_GPIO=y
 CONFIG_SYSRESET=y
 CONFIG_TIMER=y
 CONFIG_TIMER_EARLY=y