Documentation: driver-api: Move gpio.rst to gpio/index.rst

To make space for more files in the GPIO section, create a
Documentation/driver-api/gpio/ directory.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

Documentation/driver-api/gpio/index.rst

@@ -0,0 +1,45 @@
+===================================
+General Purpose Input/Output (GPIO)
+===================================
+
+Core
+====
+
+.. kernel-doc:: include/linux/gpio/driver.h
+   :internal:
+
+.. kernel-doc:: drivers/gpio/gpiolib.c
+   :export:
+
+Legacy API
+==========
+
+The functions listed in this section are deprecated. The GPIO descriptor based
+API described above should be used in new code.
+
+.. kernel-doc:: drivers/gpio/gpiolib-legacy.c
+   :export:
+
+ACPI support
+============
+
+.. kernel-doc:: drivers/gpio/gpiolib-acpi.c
+   :export:
+
+Device tree support
+===================
+
+.. kernel-doc:: drivers/gpio/gpiolib-of.c
+   :export:
+
+Device-managed API
+==================
+
+.. kernel-doc:: drivers/gpio/devres.c
+   :export:
+
+sysfs helpers
+=============
+
+.. kernel-doc:: drivers/gpio/gpiolib-sysfs.c
+   :export: