graphics/gpu-firmware-kmod: update to include more firmware files for newer and
older generations

This adds support for older generations (previously only covered by radeon) and
newer generations (vegam) alongside firmware updates and gets us in sync with
the latest Linux firmware level. While there, correct message for unsupported
releases.

With some more testing of the newer lkpi-based DRM ports, users with older HW
may opt for the modern amdgpu driver.

Reviewed by: zeising (mentor)
Approved by: zeising (mentor)
Differential Revision: https://reviews.freebsd.org/D16401