reboot: retire hw_protection_reboot and hw_protection_shutdown helpers

The hw_protection_reboot and hw_protection_shutdown functions mix
mechanism with policy: They let the driver requesting an emergency action
for hardware protection also decide how to deal with it.

This is inadequate in the general case as a driver reporting e.g. an
imminent power failure can't know whether a shutdown or a reboot would be
more appropriate for a given hardware platform.

With the addition of the hw_protection parameter, it's now possible to
configure at runtime the default emergency action and drivers are expected
to use hw_protection_trigger to have this parameter dictate policy.

As no current users of either hw_protection_shutdown or
hw_protection_shutdown helpers remain, remove them, as not to tempt driver
authors to call them.

Existing users now either defer to hw_protection_trigger or call
__hw_protection_trigger with a suitable argument directly when they have
inside knowledge on whether a reboot or shutdown would be more
appropriate.

Link: https://lkml.kernel.org/r/20250217-hw_protection-reboot-v3-12-e1c09b090c0c@pengutronix.de
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Reviewed-by: Tzung-Bi Shih <tzungbi@kernel.org>
Cc: Benson Leung <bleung@chromium.org>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Fabio Estevam <festevam@denx.de>
Cc: Guenter Roeck <groeck@chromium.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Liam Girdwood <lgirdwood@gmail.com>
Cc: Lukasz Luba <lukasz.luba@arm.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Matteo Croce <teknoraver@meta.com>
Cc: Matti Vaittinen <mazziesaccount@gmail.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Rob Herring (Arm) <robh@kernel.org>
Cc: Rui Zhang <rui.zhang@intel.com>
Cc: Sascha Hauer <kernel@pengutronix.de>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>