xfree86: fix gtf support detection for EDID 1.4.

According to the "VESA Enhanced EDID Standard", all GTF compliant 
displays are continuous frequency. 

The GTF support flags in 'Display Range Limits Descriptor' cannot be 
used if the display is a non-continuous frequency multi-mode display.
4 jobs for vitoux.pascal-master-patch-70137 in 10 minutes and 38 seconds