elsa: add systemd service and add RCONFLICTS/RREPLACES with xserver-nodm-init

* add RCONFLICTS/RREPLACES also to PN-systemd, because that's where file
  collision with xserver-nodm-init is, in PN it's just functional
  collision
* fixes upgrade path for task-x11-utils

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>