ath11k: add support for WCN6855

This patch is to add support for WCN6855. For station mode,
WCN6855 is able to connect to an AP, and ping works well.
For AP mode, hostapd is able to bringup an SAP interface with
WCN6855, a normal station can connect to this AP and
ping works well.

Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-01720.1-QCAHSPSWPL_V1_V2_SILICONZ_LITE-1
Tested-on: QCA6390 hw2.0 PCI WLAN.HST.1.0.1-01740-QCAHSTSWPLZ_V2_TO_X86-1

Signed-off-by: Baochen Qiang <bqiang@codeaurora.org>
Signed-off-by: Jouni Malinen <jouni@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210511162214.29475-7-jouni@codeaurora.org