If you are just using the RISC-V core alongside cores you've developed yourself or have licenses for, you're set. RISC-V ISA is provided. It has a very permissive, royalty-free license but you will need to become a paid member to use their trademark. I suppose they could change their license model at some point and attempt to revoke existing licenses but that would be suicide for them. Just like with all standards, there is always an IP holder but it's all a matter of how that IP is licensed out to users and the association that user can display with the IP holder. For example, you can sell a device with a Raspberry Pi inside but you can't use the HDMI trademark on your marketing materials without being a member of the HDMI Foundation.