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/Makefile b/drivers/sysinfo/Makefile
index 6d04fcb..d9f708b 100644
--- a/drivers/sysinfo/Makefile
+++ b/drivers/sysinfo/Makefile
@@ -4,5 +4,6 @@
 # Mario Six,  Guntermann & Drunck GmbH, mario.six@gdsys.cc
 obj-y += sysinfo-uclass.o
 obj-$(CONFIG_SYSINFO_GAZERBEAM) += gazerbeam.o
+obj-$(CONFIG_SYSINFO_GPIO) += gpio.o
 obj-$(CONFIG_SYSINFO_SANDBOX) += sandbox.o
 obj-$(CONFIG_SYSINFO_SMBIOS) += smbios.o