New port: graphics/gpu-firmware-kmod containing firmware kernel modules for i915, radeon, and amdgpu as obtained from and up to date with linux-firmware and to be used by the linuxkpi-based new KMS DRM.

Currently restricted to amd64 as the linuxkpi-based KMS components are similarly restricted.

Reviewed by: swills (mentor), rene (mentor), kwm, x11
Approved by: swills (mentor), rene (mentor), x11
Differential Revision: https://reviews.freebsd.org/D9931