iwlwifi: Fix and rework Kconfig file

iwlwifi: Fix and rework Kconfig file

Fixes:
- iwlwifi is an optional driver and should thus not default to 'y'.
- 3945 now depends on IWLCORE.

Rework:
- There is not a case when IWLCORE should not be selected. At the same time
  the driver does not use IWLWIFI or IWLCORE. We can just merge the usage of
  these two. With IWLWIFI being the driver name we proceed to use just it and
  replace instances of IWLCORE with it. The module name does not change
  and is still iwlcore.
- Both IWLAGN and IWL3945 are selecting FW_LOADER, we can thus just move
  this up to one select when IWLWIFI is selected.
- IWL5000 now supports Intel Wireless Wifi 100, 6000, and 6050 series.
- Now that 3945 depends on IWLWIFI we can also indicate its dependency on
  MAC80211_LEDS and LEDS_CLASS at this level.
- IWLAGN_LEDS is not used by driver - remove it.
- IWLAGN_SPECTRUM_MEASUREMENT actually depends on IWLWIFI as it forms part
  of iwlcore module. Move this config up in Kconfig to reflect that and also
  change name to IWLWIFI_SPECTRUM_MEASUREMENT.
- CONFIG_IWLWIFI_RFKILL is used by iwlagn as well as iwl3945, add text to
  description that indicates this.
- CONFIG_IWL3945_RFKILL does not exist - remove usage from driver.
- Add "iwlagn" to end of description of IWLAGN to help people understand
  what iwlagn means in rest of Kconfig text.
- Add "iwl3945" to end of description of IWL3945 to help people understand
  what iwlagn means in rest of Kconfig text.
- Change IWLWIFI_DEBUGFS description to indicate that only iwlagn supports
  it (for now).

Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>