[mtectrl] resolve race with reboot

without this change, setprop "arm64.memtag.bootctl" [...] && reboot was
racy, because it was not guaranteed that the change was applied before
rebooting.

we still immediately apply the changes as well, just in case there is
a thermal shutdown, which does not run triggers.

Bug: 256042002
Test: reboot and look at logcat
Change-Id: I9a057d4dc2e18a10f026b641f693699ae617e8ec
1 file changed