ath10k: implement mesh support

Add support for mesh to ath10k.  We simply use an AP virtual interface
in the firmware in order to enable beaconing without TSF adoption, and
use the raw (802.11) transmit mode.

Due to firmware limitations, the firmware must operate in raw
(non-native 802.11) mode.  As this is configured at firmware init time,
a new "rawmode" modparam is added, and mesh interfaces are available
only if rawmode=true.  The firmware must advertise support for rawmode;
tested successfully with firmware 10.2.4.70.6-2.

When the module is loaded with (newly implemented) modparam rawmode=1, it
will enable operating an open mesh STA via something like the following:

    ip link set wlan0 down
    iw dev wlan0 set type mp
    ip link set wlan0 up
    iw dev wlan0 set freq 5745 80 5775
    iw dev wlan0 mesh join mesh-vht

Signed-off-by: Bob Copeland <me@bobcopeland.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>