iwlwifi: PA type for 6000g2 series

For 6000g2 series of NICs, PA type is determined by uCode, driver do not
have to set the register for internal/external PA. It is a workaround
just for 6000 series NICs.

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