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