[B43]: LED triggers support

Drive the LEDs through the generic LED triggers.

Signed-off-by: Michael Buesch <mb@bu3sch.de>
Cc: Larry Finger <larry.finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>