qtwebkit: add packageconfig for qtmultimedia

Signed-off-by: Jonathan Liu <net147@gmail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
qtwebkit: fix packageconfig

Arguments passed to the qmake command-line were ignored by prf
files, which get evaluated first. QtWebKit offers QMAKE_CACHE_EVAL,
which can be used to inject a qmake snippet before anything else
gets parsed.

Signed-off-by: Andreas Oberritter <obi@opendreambox.org>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>