wl1251: remove unused definitions from wl1251_reg.h

Luis reported that IRQ_MASK conflicts with include/pcmcia/cs.h on
compat-wireless. Remove that and a bunch of other unused defines
from wl1251_reg.h.

Reported-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: Kalle Valo <kalle.valo@nokia.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>