doc: Include the I/O APIs in the documentation.

Includes the I/O drivers' interfaces in the ReST documentation.

Change-Id: I9ef70c4b0561c102b5c9425b4e41b5c813bf51b6
Signed-off-by: Rodrigo Caballero <rodrigo.caballero.abraham@intel.com>

doc/api/api.rst

@@ -19,3 +19,4 @@ The use of the Zephyr APIs is the same for all platforms and boards.
 
    nanokernel_api.rst
    microkernel_api.rst
+   io_interfaces.rst

doc/api/io_interfaces.rst

@@ -0,0 +1,65 @@
+.. _io_interfaces:
+
+Input / Output Driver APIs
+###########################
+
+.. contents::
+   :depth: 1
+   :local:
+   :backlinks: top
+
+ADC Interface
+*************
+
+.. doxygengroup:: adc_interface
+   :project: Zephyr
+   :content-only:
+
+GPIO Interface
+**************
+
+.. doxygengroup:: gpio_interface
+   :project: Zephyr
+   :content-only:
+
+I2C Interface
+*************
+
+.. doxygengroup:: i2c_interface
+   :project: Zephyr
+   :content-only:
+
+IPM Interface
+*************
+
+.. doxygengroup:: ipm_interface
+   :project: Zephyr
+   :content-only:
+
+PWM Interface
+*************
+
+.. doxygengroup:: pwm_interface
+   :project: Zephyr
+   :content-only:
+
+Pinmux Interface
+****************
+
+.. doxygengroup:: pinmux_interface
+   :project: Zephyr
+   :content-only:
+
+SPI Interface
+*************
+
+.. doxygengroup:: spi_interface
+   :project: Zephyr
+   :content-only:
+
+UART Interface
+**************
+
+.. doxygengroup:: uart_interface
+   :project: Zephyr
+   :content-only: