iwl3945: Use iwlcore TX queue management routines

By adding an additional hw_params (tfd_size) and a new iwl_lib ops (txq_init),
we can now use the iwlcore TX queue management routines.
We had to add a new hw_params because we need to allocate the right DMA buffer
for TFDs, and those have a different sizes depending if you're on 3945 or agn.

Signed-off-by: Samuel Ortiz <samuel.ortiz@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>