iwl3945: rearrange 3945 tfd

This patch moves 3945 TFD structures to iwl-3945-fh.h. It renames them
similarly to AGN naming. This patch also eliminates iwl3945_tx_info and
fixes endianity issue in iwl3945_tx_skb and iwl3945_enqueue_hcmd caused
by ugly casting.

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