iwlwifi: HT antenna/chains overhaul

1. This patch restructures rate scale algorithm to support
   SISO, MIMO2, MIMO3
2. It adds support for detailed valid TX and RX antennas settings
3. It removes few unesfull antenna definitions

Signed-off-by: Guy Cohen <guy.cohen@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>