virtio_gpu: add support for xf86-video-scfb
Added virtio_gpu support for UTM/MacOS configured with virtio-gpu-pci.
Tunable parameters:
- hw.virtio_gpu.width
- hw.virtio_gpu.height
- dev.vtgpu.X.refresh_rate
Tested with FreeBSD 15 (arm64) running on MacOS 26.2 and UTM (version 4.7.5 / qemu 10.0.2).