libv4l: bump version to 1.8.0

- add qt, qt5base/qt5gui/qt5widgets dependency for qv4l2
  (qt dependency was missing, qt5 support was added since 1.8.0)

- fix fix moc/rcc/uic detection in case host versions
  of moc-qt5, rcc-qt5 or uic-qt5 are present

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>