wcn36xx: Disable bmps when encryption is disabled

For whatever reason, when connected to an open/no-security BSS,
the wcn36xx controller in bmps mode does not forward 'wake-up'
beacons despite AP sends DTIM with station AID.

Meaning that AP is not able to wakeup the station and needs to wait
for the station to wakeup by its own (TX data, keep alive pkt...),
causing serious latency issues and unexpected deauth.

When connected to AP with encryption enabled, this issue does not occur.
So a simple workaround is to only enable bmps support in that case.

Ideally, it should be propertly fixed to allow bmps support with open
BSS, whatever the issue is at driver or firmware level.

Tested on wcn3620 and wcn3680.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Tested-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/1598363127-26066-1-git-send-email-loic.poulain@linaro.org