kconfig: refer to qt3 if we cannot find qt libraries

We do not support qt4 (yet) so the simple fix was to warn
that qt3 are missing.
The better fix would have been to implment qt4 support
but that has failed so far.

This solves http://bugzilla.kernel.org/show_bug.cgi?id=8277



Signed-off-by: Sam Ravnborg <sam@ravnborg.org>