iwlwifi: 3945 extract flow handler definitions into iwl-3945-fh.h

This patch moves 3945 definitions into iwl-3945-fh.h
It renames FH_ to FH39 to help inclusion of 3945 into iwlcore
framework

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>