Support building wl1271-equipped boards without building the
wl1271 driver itself, e.g.:

CONFIG_MACH_OMAP_ZOOM3=y
CONFIG_WL12XX is not set
Reported-by: NJohn W. Linville <linville@tuxdriver.com>
Signed-off-by: NOhad Ben-Cohen <ohad@wizery.com>
Signed-off-by: NLuciano Coelho <luciano.coelho@nokia.com>