Well, gfxutil will show you correct path to GFX0. You have to insert it in DeviceProperties like on my screenshot. Just drag binary file on Terminal and press Return button.
SSDT-BRG0 is used to assign bridge name for your card. All Radeon cards starting from Vega works through extra bridge. You can see it in IOReg (PEG1->PEGP->pci-bridge->GFX0). In order to inject DeviceID to GFX0 you need to determine pci-bridge device in ACPI. If you did it correct your IOReg should look like this
View attachment 524909
Without this SSDT your deviceID for GFX0 will not be injected.
Also short description of this fix described in
SSDT-BRG0 source code.