pinephone: suspend does not work with elogind

While investigating on #676 (closed), I've tried suspending my BraveHeart PinePhone with loginctl suspend, which is the elogind equivalent of systemctl suspend.

After doing loginctl suspend the phone does not sleep and the screen stays on.

On dmesg I get this:

[  153.346425] elogind-daemon[2645]: Suspending system...
[  153.346528] PM: suspend entry (deep)
[  153.500934] Filesystems sync: 0.154 seconds

Also, after doing loginctl suspend the phone goes in a weird state where software poweroff and reboot do not work anymore,
so I have to remove the battery to recover the phone.

This behaviour is confirmed by @dusxmt on UBPorts CE PinePhone.

Note: I've tested on v20.05 at commit a313b703