ath11k-qca6390-bringup-202012140938: rebate to v5.10 and MHI M2 workaround

[Stephen Liang]

Uptime has been very good so far at 24 hours, no hangs. I did see a
backtrace when associating with a different AP, please see:
https://pastebin.com/raw/5VTAK1mp

This backtrace does not appear to affect functionality and the AP
associates just fine.

Speedtest.net is giving me 340 mbps down / 185 mbps up, so very good
throughput. I can do a LAN iperf throughput test later on as well if
there's interest.

> * name of the bringup branch tag you used

ath11k-qca6390-bringup-202012140938

> * if there are other changes in the kernel, patches, reverts etc

Clean copy of Fedora rawhide kernel 5.10.0-0.rc6.20201202git509a15421674.91

> * do you use the memmap kernel parameter

No

> * make and model of the laptop/computer (eg. Dell XPS 13 9310)

Dell XPS 9310

> * how much testing you did

Mixed usage, suspend, wake, charge, discharge, etc. WiFi network
disassociate and associate, etc.