board: add support for Banana Pro

board: add support for Banana Pro

The board support package includes the following components:
 - U-Boot 2016.11
 - Linux 4.9.3
 - packages:
   - alsa-utils for basic audio usage of the on-board headphone jack
     and microphone
   - iw and wpa_supplicant for managing the wireless interface

Two Linux patches are necessary to enable audio and wifi support. Both
patches are fetched from the Linux next branch and are probably mainlined in
Linux 4.11.

A Linux configuration fragment enables the wireless device driver, which
is not enabled by default in the mainline defconfig of the board.

The wifi chip needs a NVRAM configuration file which is provided in the
rootfs overlay.

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
[Thomas: remove e2fsprogs from the target packages, add entry in
DEVELOPERS file, remove C++ support.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>