firmware: ti_sci: Use devm_register_restart_handler()

Use device life-cycle managed register function to simplify probe.

Signed-off-by: Andrew Davis <afd@ti.com>
Reviewed-by: Gabriel Somlo <gsomlo@gmail.com>
Reviewed-by: Markus Schneider-Pargmann <msp@baylibre.com>
Link: https://lore.kernel.org/r/20240326223730.54639-2-afd@ti.com
Signed-off-by: Nishanth Menon <nm@ti.com>