battery switch-over detection on pcf2127

[Rasmus Villemoes]

Hi Bruno

I just noticed your "rtc: pcf2127: add tamper detection support"
(03623b4b04) from 5.4. Unfortunately, clearing the BTSE bit breaks a use
case of ours:

We rely on the battery switch-over detection to distinguish a powerfail
during boot from a PORESET by the external watchdog (in the latter case,
the RTC is still powered throughout, meaning there is no battery
switch-over event). OTOH, we do not use the tamper detection - in fact,
the TS signal is unconnected on our board.

We're currently still on 4.19, but we will eventually upgrade to a
kernel containing the above commit. So I was wondering if we could
figure out a way that would work for both of us - either some CONFIG
knob, or perhaps something in the device-tree. Any ideas?

Rasmus