The Ironic bios API - /v1/nodes/{node_ident}/bios, has been available since version 1.40 of the Ironic API, see
https://docs.openstack.org/api-ref/baremetal/?expanded=#node-bios-nodes. It provides the ability to get all or individual BIOS settings on a node.

Support should be added to Gophercloud for the bios API.