package/systemd: create groups required for udevd

udevd needs extra groups for its bundled rules:

    Mar 03 12:21:30 buildroot systemd-udevd[732]: Specified group 'render' unknown
    Mar 03 12:21:30 buildroot systemd-udevd[732]: Specified group 'kvm' unknown

Add those missing groups.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Cc: Julius Kriukas <julius@kriukas.lt>
Cc: Trent Piepho <tpiepho@impinj.com>
Cc: Adam Duskett <aduskett@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>