x11-servers/xorg-server: Update to 1.20.8

Update x11-servers/xorg-server to 1.20.8
This is a maintenance release
Most notably, fixes some issues with displayport MST
improves glamor in oom situations

Add a patch to make us more compatible with the linux evdev headers
we're using (devel/evdev-proto). This is needed for xf86-video-qxl.

complete changelog:
https://lists.x.org/archives/xorg-announce/2020-March/003041.html

Obtained from: https://github.com/FreeBSDDesktop/freebsd-ports/tree/feature/xserver-1.20