Separated the MIMO tpt matrix into MIMO2 and MIMO3, adding MIMO3 support
in rate scaling algorithm. If the device support 3x3, then utilize all
three antenna (A/B/C) for tx to improve throughput.

Adding rs_switch_to_mimo3() function to allow switch to mimo3 modulation
mode from other modes(legacy/siso/mimo2). Adding rs_move_mimo3_to_other()
function to allow switch from mimo3 modulation mode to either siso or mimo2;
also support toggle between SGI and NGI.
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>