iwlwifi: pass the iwl_config_trans_params when needed

Instead of accessing the iwl_config_trans_params from the cfg that is
stored in the trans struct, pass this structure directly to functions
that need it during trans_alloc.  This will be useful to isolate the
elements needed during allocation and pass them separately before the
actual cfg struct is known.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>