gpio: ABI: mark the sysfs ABI as obsolete

This marks the (optional) sysfs GPIO ABI as obsolete and schedules
it for removal in 2020.

Cc: Johan Hovold <johan@kernel.org>
Cc: Michael Welling <mwelling@ieee.org>
Cc: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/MAINTAINERS b/MAINTAINERS
index a85cd6d..7df638b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4816,6 +4816,7 @@
 S:	Maintained
 F:	Documentation/gpio/
 F:	Documentation/ABI/testing/gpio-cdev
+F:	Documentation/ABI/obsolete/sysfs-gpio
 F:	drivers/gpio/
 F:	include/linux/gpio/
 F:	include/linux/gpio.h