systemd: add group render to udev package

From NEWS for v236:
* The "uaccess" udev tag has been dropped from /dev/kvm and
  /dev/dri/renderD*.  These devices now have the 0666 permissions by
  default (but this may be changed at build-time). /dev/dri/renderD*
  will now be owned by the "render" group along with /dev/kfd.

Without the group systemd-udevd startup logs:
  /lib/udev/rules.d/50-udev-default.rules:39 Unknown group 'render', ignoring
  /lib/udev/rules.d/50-udev-default.rules:40 Unknown group 'render', ignoring

Signed-off-by: Peter Marko <peter.marko@siemens.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>