watchdog: rn5t618: add support for read out bootstatus

The PMIC does store the power-off factor internally.
Read it out and report it as bootstatus.

Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
Acked-by: Lee Jones <lee@kernel.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20221028075019.2757812-1-marcus.folkesson@gmail.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>