iwl3945: use iwl_led structure

3945 can now use iwl_led's structure from iwlwifi.
Patch also removes CONFIG_IWL3945_LEDS flag from Kconfig as 3945's led
support will now be enabled if user selects CONFIG_IWLWIFI_LEDS.

Signed-off-by: Abhijeet Kolekar <abhijeet.kolekar@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>