firmware: arm_scmi: Add SCMI v3.1 VOLTAGE_LEVEL_SET_COMPLETE

Add SCMI v3.1 voltage protocol support for asynchronous VOLTAGE_LEVEL_SET
command.

Note that, if a voltage domain is advertised to support the asynchronous
version of VOLTAGE_LEVEL_SET, the command will be issued asynchronously
unless explicitly requested to use the synchronous version by setting the
mode to SCMI_VOLTAGE_LEVEL_SET_SYNC when calling voltage_ops->level_set.

The SCMI regulator driver level_set invocation has been left unchanged
so that it will transparently use the asynchronous version if available.

Link: https://lore.kernel.org/r/20220330150551.2573938-21-cristian.marussi@arm.com


Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>