iwlwifi: merge and better support of suspend/resume for iwlagn and iwl3945

With mac80211's help to call stop() and start() in mac80211
suspend/resume function, both iwlagn and iwl3945 no longer calling
stop() and start(); remove un-necessary STATUS_IN_SUSPEND bit from both
header files and functions,

Move apm_ops.stop() function into pci_suspend() to ensure
DMA is stopped before go into suspend mode.

iwl3945 has the similar suspend/resume function as iwlagn, so move both
functions to iwlcore to be shared by both drivers.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>