Migrate SSRS Reports to Power BI Report Server
...is there any way that I can put these services in the same 
  server/database and running under the Power BI Report Server?


You can have SSRS and PBIRS on the same Server, but they will require their own ReportServer databases in order to run them both. 

If you want to migrate your SSRS reports into PBIRS, then you need to follow the steps in the MS article. 1. Restore a copy of the SSRS database to a new server, and then 2. install PBI RS. PBI RS will update the database and retain the reports within it. 

I think the article gets a little confusing as most people reading it will be migrating from SSRS to PBIRS on a different SQL Server. There isn't a lot of info about running both side by side. But it can be done.