Up to now the LinuxKPI wlan drivers were using local variables starting
with a WITH_ prefix. That is likely to collide with other mechanisms
like WITH_ and WITHOUT_ from src.conf. Adjust the local variables to
use a driver name prefix for now to control what is built and what is
not. These variables are mainly for the time of development so we can
turn off/on a feature or bus attachment while working on it. Otherwise
they are there for documentation purposes. The only reason one would
change them locally would be if someone was to build a very custom
image and not want certain bits (e.g., USB support) being compiled into
the modules.

While here, try to harmonize some parts of the Makefiles.

Suggested by: imp
Discussed with: imp
Sponsored by: The FreeBSD Foundation
MFC after: 3 days