iwlwifi: reorganize flow handler bitology

This patch cleans up FH bits and adds missing register values
that will be used later in TX initialization rewrite

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