iwlwifi: remove host commands structures from iwl_cmd

This patch removes host commands structures from iwl_cmd
to make more HW oblivious
tx cmd was left it needs special treatment.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Reviewed-by: Zhu Yi <yi.zhu@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>