QSV: move LookAheadDepth miminum to commmon code.

Unlike the maximum limit, which is HandBrake-specific, this is not our bug, and we can't fix it, short of dropping support for all old Haswell drivers.



git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@5813 b64f7644-9d1e-0410-96f1-a4d463321fa5