hwmon: (dell-smm) Prepare for multiple SMM calling backends

hwmon: (dell-smm) Prepare for multiple SMM calling backends

Modern Dell machines support multiple ways to issue an SMM call.
Prepare support for those by introducing dell_smm_ops, which is
used by dell_smm_call() to perform a SMM call. Each SMM backend
needs to provide a dell_smm_ops structure.

Tested-by: <serverror@serverror.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://lore.kernel.org/r/20231123004820.50635-2-W_Armin@gmx.de
Signed-off-by: Guenter Roeck <linux@roeck-us.net>