iwlagn: add IQ inversion support for 2000 series devices

The I/Q swapping is extremely important and should be dealt with extra care.
It will affects OFDM and CCK differently.

For 6000/6005/6030 series devices, the I/Q were swapped, and for 2000 series
devices, it is in non-swapped status (but its swapped with respected to 6000/6005/6030).
so the CSR_GP_DRIVER_REG_BIT_RADIO_IQ_INVER register need to be set to support
the correct behavior.

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>