buildroot

package/qt5/qt5scxml: needs qt5declarative package

qt5scxml package needs qml-private module which is delivered by
qt5declarative.

Fixes:

  http://autobuild.buildroot.net/results/9e650f6147f7858be74782806f4b8d2aac4c689a/

Signed-off-by: Bartosz Bilas <b.bilas@grinn-global.com>
[Thomas: add missing dependency on BR2_PACKAGE_QT5_JSCORE_AVAILABLE,
adjust commit log.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>