xorg: upgrade to 21.1.4

Port changes:
- flavorize the port
- decouple Xwayland as it has been split from Xorg
- switch to meson
- cleanup non necessary patches anymore
- stop butchering the build system to play with Xorg.wrap but do it
  in post-install
- remove dmx (no longer existing)
- use libmd for sha1 (remove dependency on open/libre ssl)
- always activate RPC security
- simplify postinstall/deinstall script and make them cross install friendly
- remove the SUID option and make it the default, we cannot startx as user without it
- only keep the mesa-dri dependency on xorg-server not others

xf86-video-ati: fix build with recent xorg

While here incorporate a patch which prevent crash of the driver
when xrandr is invoked

Update x11/libxcvt to provide cvt(1) and friends which are not provided anymore
Xorg

Reviewed by:		tcberner, manu, jbeich
Approved by:		tcberner, manu
Differential Revision:	https://reviews.freebsd.org/D35661