qtwayland: respect OE_QMAKE_PATH_QT_HEADERS and use QT_VERSION variable
qtwayland: respect OE_QMAKE_PATH_QT_HEADERS and use QT_VERSION variable

* QT_VERSION allows to use 5.3.1 e.g. when overriding SRCREV
* ${includedir}/${QT_DIR_NAME} is the default value of OE_QMAKE_PATH_QT_HEADERS, but
  when it's changed by user we should respect it here

Signed-off-by: Martin Jansa <516df3ff67e1fa5d153800b15fb204c0a1a389dc@gmail.com>

cjp256/meta-qt5,timopulkkinen/meta-qt5,jruffin/meta-qt5,Ivan-SB/meta-qt5,kraj/meta-qt5,sapiippo/meta-qt5,schnitzeltony/meta-qt5,opendreambox/meta-qt5,jruffin/meta-qt5,Tofee/meta-qt5,kraj/meta-qt5,meta-qt5/meta-qt5,opendreambox/meta-qt5,cjp256/meta-qt5,schnitzeltony/meta-qt5,timopulkkinen/meta-qt5,sapiippo/meta-qt5,meta-qt5/meta-qt5,Tofee/meta-qt5,Ivan-SB/meta-qt5,timopulkkinen/meta-qt5,opendreambox/meta-qt5,timopulkkinen/meta-qt5