ath11k: Add support for WCN6750 device

WCN6750 is non-DBS 2x2 11AX chipset. Unlike QCA6390 which is a
DBS (dual band simultaneous) solution (2 LMACs), WCN6750 has a
single LMAC supporting 2G, 5G and 6G bands but will operate only
on one band at any given point.

WCN6750 is a PCIe based solution, but it is attached to the WPSS
(Wireless Processor SubSystem) Q6 processor, hence it is enumerated
by the Q6 processor. It is registered to the APSS processor
(Application Processor SubSystem) as a platform device(AHB) and
remoteproc APIs are used to boot up or shutdown the device like
other AHB devices.

Also, Device information like BAR and it's size is not known to the
APSS processor as the chip is enumerated by WPSS Q6. These details
are fetched over QMI.

STA and AP modes are supported. Verified basic connectivity and ping
in both the modes.

An important point to note is that though WCN6750 is a PCIe device,
it cannot be attached to any other platform except on Qualcomm
Snapdragon SoCs due to the aforementioned reasons.

Tested-on: WCN6750 hw1.0 AHB WLAN.MSL.1.0.1-00887-QCAMSLSWPLZ-1
Tested-on: WCN6855 hw2.0 PCI WLAN.HSP.1.1-01720.1-QCAHSPSWPL_V1_V2_SILICONZ_LITE-1
Tested-on: QCN9074 hw1.0 PCI WLAN.HK.2.5.0.1-01100-QCAHKSWPL_SILICONZ-1
Tested-on: IPQ8074 hw2.0 AHB WLAN.HK.2.4.0.1-00192-QCAHKSWPL_SILICONZ-1

Signed-off-by: Manikanta Pubbisetty <quic_mpubbise@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20220429170502.20080-10-quic_mpubbise@quicinc.com