iwlwifi: consolidate apm_init() functions

Consolidate most iwlXXXX_apm_init() functions into single iwl_apm_init().
Keep iwl3945_apm_init(), but leverage iwl_apm_init() for most functionality.
Update 4965 init sequence to follow most recent factory recommendations.

Add following members to struct iwl_cfg to guide the init sequence:
pll_cfg_val (replaces needs_pll_cfg), set_l0s, use_bsm

Move L0S enable/disable from nic_config() functions to iwl_apm_init().
This satisifies the "FIXME: put here L1A -L0S w/a" notice, and complies
with factory-recommended sequence.

Add debug info message in iwl_apm_init(), and symmetrical message
in iwl_apm_stop().

Signed-off-by: Ben Cahill <ben.m.cahill@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>