qt5multimedia: Make it compile with no-opengl

Backport an upstream patch to make it compile with no-opengl. Otherwise
it will fail showing an error message like this one:

qpaintervideosurface.cpp:99:47: error: 'QOpenGLContext' has not been
declared

Upstream commit:

  https://qt.gitorious.org/qt/qtmultimedia/commit/2b181d546970d18a48a0f36f5d1a22418b61cd4d

Fixes:

  http://autobuild.buildroot.net/results/b77/b77cdf9b1cf6cafd5afef7337553bb32489207e5/



Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>