[oe] Qt4 recipes and sql drivers

[Ihar Hrachyshka]

Hello guys!
For my work project, I need to use Qt with Postgres and possibly
Sqlite. For this I modified current qt4.inc configure options and
DEPENDS. Seems to work fine.
The question is: should I enable functional sql drivers (as plugins of
course) in-tree? The only problem I see here is that compile time for
qt4 recipes will be a little longer (to build postgres and sqlite),
but runtime dependencies are not bloated with postgres/sqlite things
unless you really install the affected sqldrivers packages. If you
will approve this change then I'll send a patch to ML.
Thanks.