banana_pi.md: Added documentation for BananaPi/Pro

Signed-off-by: Michael Ring <mail@michael-ring.org>
Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>

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+Banana Pi/Pro    {#bananapi}
+============
+
+The Banana Pi/Pro is a clone of the well known Raspberry Pi. It has advantages
+compared to the 'old' Raspberry Pi A/B/A+/B+ devices as it is based on the
+Allwinner A20 Dual Core Cortex-A7. It also has 1G Ethernet compared to 100M
+Ethernet on the Raspberry.
+
+There is a lot of effort on Mainline Kernel to fully support the Allwinner
+Chips, for example Fedora 22 Arm will come with support for BananaPi/Pro which
+means that you will be able to have HDMI Output and a number of periperal
+modules work out of the box.
+
+Pin-wise the Banana Pi matches the Raspberry Pi, the Banana Pro has a connector
+similar to the Raspberry Pi A+/B+
+
+Revision Support
+----------------
+Banana Pi
+Banana Pro
+
+Interface notes
+---------------
+
+**PWM** Whilst the Banana Pi is meant to have 1 PWM channel this is currently
+not supported.
+
+**SPI** works fine when used with old 3.4 Kernels provided by Lemaker, on
+Mainline Kernel SPI does currently not work
+
+**COM** I have created devicetree patches so that Mainline Kernel supports all
+COM-Interfaces, this is not yet visible in Kernel
+
+Mainline Kernel requires the use of Device-Trees, mraa tries it's best to guess
+which gpio/serial/i2c/spi is connected where but there is currently no support
+to manipulate the Device-Tree settings from within mraa. If a device does not
+work as expected then please check syslog, mraa usually complains with a
+meaningful message when it is unable to initialize the device.
+
+Pin Mapping
+-----------
+
+This pin mapping refers to the Banana Pi but gives an idea
+as to what the values are from mraa. Note that there is an emum to use wiringPi
+style numbers.
+
+| MRAA Number | Physical Pin | Function  |
+|-------------|--------------|-----------|
+| 1           | P1-01        | 3V3 VCC   |
+| 2           | P1-02        | 5V VCC    |
+| 3           | P1-03        | I2C SDA   |
+| 4           | P1-04        | 5V VCC    |
+| 5           | P1-05        | I2C SCL   |
+| 6           | P1-06        | GND       |
+| 7           | P1-07        | GPIO(PI03)|
+| 8           | P1-08        | UART4 TX  |
+| 9           | P1-09        | GND       |
+| 10          | P1-10        | UART4 RX  |
+| 11          | P1-11        | GPIO(PI19)|
+| 12          | P1-12        | GPIO(PH02)|
+| 13          | P1-13        | GPIO(PI18)|
+| 14          | P1-14        | GND       |
+| 15          | P1-15        | GPIO(PI17)|
+| 16          | P1-16        | GPIO(PH20)|
+| 17          | P1-17        | 3V3 VCC   |
+| 18          | P1-18        | GPIO(PH21)|
+| 19          | P1-19        | SPI MOSI  |
+| 20          | P1-20        | GND       |
+| 21          | P1-21        | SPI MISO  |
+| 22          | P1-22        | GPIO(PI16)|
+| 23          | P1-23        | SPI SCL   |
+| 24          | P1-24        | SPI CS0   |
+| 25          | P1-25        | GND       |
+| 26          | P1-26        | SPI CS1   |
+
+There is also a second 8-pin connector on the Banana Pi, the pins are as follows:
+
+| 27          | P1-19        | 5V VCC    |
+| 28          | P1-20        | 3V3 VCC   |
+| 29          | P1-21        | GPIO(PH5) |
+| 30          | P1-22        | GPIO(PI22)|
+| 31          | P1-23        | GPIO(PH03)|
+| 32          | P1-24        | GPIO(PI20)|
+| 33          | P1-25        | GND       |
+| 34          | P1-26        | GND       |