Rename the wifi-firmware-base to wifi-firmware-kmod (similar to
gpu-firmware-mod). Make the new subdir a metaport including all
wireless firmware.
Move the old Makefile to Makefile.inc and adjust the child ports
accordingly.
This solves two problems: (1) the base port is buildable and (2)
there is a single port to depend on to add all the needed firmware
files to, e.g., put on a release media.
Suggested by: amdmi3
PR: 270742