firmware_class: Refer to Debian wiki page when logging missing firmware

firmware_class: Refer to Debian wiki page when logging missing firmware

Bug-Debian: https://bugs.debian.org/888405
Forwarded: not-needed

If firmware loading fails due to a missing file, log a second error
message referring to our wiki page about firmware.  This will explain
why some firmware is in non-free, or can't be packaged at all.  Only
do this once per boot.

Do something similar in the radeon and amdgpu drivers, where we have
an early check to avoid failing at a point where we cannot display
anything.

Gbp-Pq: Topic debian
Gbp-Pq: Name firmware_class-refer-to-debian-wiki-firmware-page.patch