@JiriLio
OOTB turnkey set-ups have MySQL configured as the dependent service for JBoss service i.e JBoss will wait for MySQL to come up before starting the server.
I didn't get the question actually- do you want to decouple the dependency or couple the two?
Go to JBoss service properties in the services.msc and then dependencies, you will be able to couple/decouple the MySQL service.