x11/nvidia-driver: Add Makefile.version and patch for nvidia-drm
This moves the version string into a makefile that can be included from
child ports.
This also adds a patch to nvidia-modeset that handles a deadlock with
queueing events observed with nvidia-drm. This fix is only needed in
535, future versions will have a proper implementation included with
them.
Approved by: maintainer timeout
Differential Revision: https://reviews.freebsd.org/D40168