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>
diff --git a/drivers/net/wireless/iwlwifi/iwl-csr.h b/drivers/net/wireless/iwlwifi/iwl-csr.h
index 6c2b2df..f52bc04 100644
--- a/drivers/net/wireless/iwlwifi/iwl-csr.h
+++ b/drivers/net/wireless/iwlwifi/iwl-csr.h
@@ -382,6 +382,8 @@
 #define CSR_GP_DRIVER_REG_BIT_CALIB_VERSION6	    (0x00000004)
 #define CSR_GP_DRIVER_REG_BIT_6050_1x2		    (0x00000008)
 
+#define CSR_GP_DRIVER_REG_BIT_RADIO_IQ_INVER	    (0x00000080)
+
 /* GIO Chicken Bits (PCI Express bus link power management) */
 #define CSR_GIO_CHICKEN_BITS_REG_BIT_L1A_NO_L0S_RX  (0x00800000)
 #define CSR_GIO_CHICKEN_BITS_REG_BIT_DIS_L0S_EXIT_TIMER  (0x20000000)