[v2] Xext: vidmode: simplify dispatcher
These dispatcher functions are much more complex than they're usually are (just switch/case statement). Bring them in line with the standard scheme used in the Xserver, so further steps become easier.
Also a preparation for #1701
changes v2:
- resolved conflicts
- removed VLAs in structs
Edited by Enrico Weigelt, metux IT consult .