Moving wayland plugin to the qtwayland submodule

Moving wayland plugin to the qtwayland submodule

The wayland platform plugin now lives in its own Qt module, together with
the qtcompositor library.

Change-Id: I4e85292cf41da4ef021ea832545ac37f5ed4e991
Reviewed-on: http://codereview.qt-project.org/5836
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>
Reviewed-by: Andy Nichols