sysinfo: Add gpio-sysinfo driver

This uses the newly-added dm_gpio_get_values_as_int_base3 function to
implement a sysinfo device. The revision map is stored in the device tree.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/sysinfo/Kconfig b/drivers/sysinfo/Kconfig
index 85c1e81..381dcd8 100644
--- a/drivers/sysinfo/Kconfig
+++ b/drivers/sysinfo/Kconfig
@@ -30,4 +30,12 @@
 	  one which provides a way to specify this SMBIOS information in the
 	  devicetree, without needing any board-specific functionality.
 
+config SYSINFO_GPIO
+	bool "Enable gpio sysinfo driver"
+	help
+	  Support querying gpios to determine board revision. This uses gpios to
+	  form a ternary number (when they are pulled-up, -down, or floating).
+	  This ternary number is then mapped to a board revision name using
+	  device tree properties.
+
 endif