I have built the gvt-staging, but after booting with required kernel parameters (see below) mdev_supported_types does not appear. Dmesg prints the error (see also DmesgGvtStaging.txt):

i915 0000:00:02.0: Direct firmware load for i915/gvt/vid_0x8086_did_0x3e9b_rid_0x00.golden_hw_state failed with error -2

System: Arch Linux
CPU: Coffee Lake (i7-8750H)
GPU: Optimus (UHD Graphics 630 + Quadro P600)
Driver: bumblebee 3.2.1-20 xf86-video-intel 1:2.99.917+860+g3a2dec17-1 nvidia-dkms 418.43-4
Branch: gvt-staging (built 03.03.19)
Kernel Parameters for dmesg: i915.enable_gvt=1 kvm.ignore_msrs=1 intel_iommu=on ignore_loglevel drm.debug=2 "dyndbg=file gvt +p"