ati-spi2-core: new package.

The ati-spi2-core package provides Assistive Technology Service Provider
Interface (dbus core). This package is a requirement for Gtk+ 3.0.
at-spi2-atk: new package.

The at-spi2-atk package provides AT-SPI 2 Toolkit Bridge. This is a
requirement for Gtk+ 3.0.
pango: bump to 1.32.6.

This is a requirement for Gtk+ 3.0.
libgtk3: new package.

This is package provides Gtk+ version 3, a toolkit for creating
graphical user interfaces. The current version is Gtk+ 3.8.
board: add elebihan demo-gtk3-x11 and demo-gtk3-wayland.

New configuration files are available to build a kernel and file system to
showcase Gtk+ 3.0 either with X11 or Wayland backends, on a QEMU virtual
machine (x86 or ARM).