wl12xx: change WLVIF_FLAG_PSM name and remove WLVIF_FLAG_PSM_REQUESTED

WLVIF_FLAG_PSM turned to WLVIF_FLAG_IN_AUTO_PS which
marks that this vif is in AUTO PS.

WLVIF_FLAG_PSM_REQUESTED is not required as mac80211
calls op_config with CONF_PS after association.

wl12xx_config_vif() handling of CONF_PS was simplified
and cleaned up.

Signed-off-by: Eyal Shapira <eyal@wizery.com>
Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>