Remove unnecessary includes from base.h.  Add includes to other files as
necessary.  Don't include base.h unless needed.

Move declarations for functions in base.c from ath5k.h to base.h.

Use a better named define to protect base.h against double inclusion.
Signed-off-by: NPavel Roskin <proski@gnu.org>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>