power: reset: msm-poweroff: Use devm_register_sys_off_handler(POWER_OFF)

Use this helper to register sys_off handler. Drivers should move away from
setting pm_power_off directly as it only allows for one handler. The new
way allows for trying multiple if the first one doesn't work.

Signed-off-by: Andrew Davis <afd@ti.com>
Link: https://lore.kernel.org/r/20240212162831.67838-13-afd@ti.com


Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>