power: reset: nvmem-reboot-mode: quiet some device deferrals

Some errors are being logged that are really due to deferrals,
which is confusing to users. Use dev_err_probe() to handle when to log
at error level versus debug. This also has the added bonuses of logging
to devices_deferred and printing the error value.

Signed-off-by: Andrew Halaney <ahalaney@redhat.com>
Reviewed-by: Brian Masney <bmasney@redhat.com>
Tested-by: Brian Masney <bmasney@redhat.com>
Link: https://lore.kernel.org/r/20230817214218.638846-1-ahalaney@redhat.com
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

power: reset: nvmem-reboot-mode: use NVMEM as reboot mode write interface

Add a new reboot mode write interface that is using an NVMEM cell
to store the reboot mode magic.

Signed-off-by: Nandor Han <nandor.han@vaisala.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>