wil6210: enable AP/PCP power save

New FW has power save capability in AP/PCP mode. FW reports this to
driver with WMI_FW_CAPABILITY_AP_POWER_MANAGEMENT.

AP/PCP mode power save in FW is disabled by default. It can be enabled
by sending WMI_PS_DEV_PROFILE_CFG_CMD to FW as part of start_ap
sequence.

Several pre-conditions must be met for driver to enable this:
1. power save enabled from cfg80211
2. AP power save enabled from platform driver. This is reported from
   platform driver with a new WIL_PLATFORM_CAPA_AP_PS

AP power save can be controlled via "ap_ps" debugfs.

Change-Id: I328fdbfe5382e60688c9f4a67aa9378197e01987
Signed-off-by: Ahmad Masri <amasri@codeaurora.org>