graphics/gpu-firmware-kmod: Fix build as user, install more radeonkms firmware.

Add uidfix (originally suggested by kwm, noted later independently by jbeich in PR 221915 and jkim) and install more radeonkms firmware files as by drm-next pull request from jkim.

PR: 221915
Reviewed by: swills (mentor)
Approved by: swills (mentor)
Obtained from: https://github.com/FreeBSDDesktop/freebsd-base-graphics [jkim] , kwm
Differential Revision: https://reviews.freebsd.org/D12158