iwlwifi: separate nic_config for different NIC

Different NIC has different requirements for configuration. Currently all
5000 series hardware and later share the same configuration function even
though they do not need the same configurations. Fix this by separating the
needed configuration actions for each hardware model.

.5000 series: L1-ASPM H/W bug work-around
              configure radio
              write CSR_HW_IF_CONFIG_REG for uCode use
              work-around for NIC get stuck after early PCIe power off

.1000 series: write CSR_HW_IF_CONFIG_REG for uCode use
              setting digital SVR for 1000 card to 1.32V

.6000 series: configure radio
              write CSR_HW_IF_CONFIG_REG for uCode use
              write CSR_GP_DRIVER_REG to indicate radio sku

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>