Use QSVHelper utilities in Encoder_QSV.cpp

Utilities.h will now also undefine min/max macros so std::min/std::max and
similar functions can be used
Fix an issue with OBS to QSV bitrate conversion

Also log a warning if (user) configured bitrate exceeds maximum QSV bitrate
(maximum QSV bitrate is 2**16-1 = 65535)