iwlagn: enable shadow register

For 6000 series devices and up, enable automatic update MAC's register
for better power usage in PSP mode

Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

diff --cc drivers/net/wireless/iwlwifi/iwl-6000.c
Simple merge

diff --cc drivers/net/wireless/iwlwifi/iwl-agn-lib.c
Simple merge

diff --cc drivers/net/wireless/iwlwifi/iwl-core.h
Simple merge

diff --cc drivers/net/wireless/iwlwifi/iwl-csr.h
Simple merge

diff --cc drivers/net/wireless/iwlwifi/iwl-rx.c
Simple merge

diff --cc drivers/net/wireless/iwlwifi/iwl-tx.c
Simple merge