net/wifi-firmware-*: use metaport for "base" and switch to Makefile.inc

Rename the wifi-firmware-base to wifi-firmware-kmod (similar to
gpu-firmware-mod).  The former was never build so technically it
is no move.  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 now 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
Reviewed by:	ehaupt, jrm
Approved by:	ehaupt, jrm
Differential Revision: https://reviews.freebsd.org/D40014

net/wifi-firmware-*: add framework and firmware for various WiFi chipsets

Add a "base port framework" to fetch (WiFi) firmware and license files
from the linux-firmware.git repository and an accompanying FreeBSD
build kmod framework tarball (for now; we might do without that in
the future).
Add child ports for Realtek rtw88 and rtw89, Mediatek mt76, and
Atheros ath10k and ath11k firmware as a start.

This is a beginning in order to stop bloating src.git and the
installed kernels with lots of MB of firmware files whereas usually
only one vebdor/chipset/flavor is needed.  Before fully switching
more infrastructure needs to be in place but this is the first and
most important step.

PR:		270742
Reviewed by:	lwhsu
Approved by:	lwhsu (ports)
Differential Revision: https://reviews.freebsd.org/D39487