iio/scmi: Port driver to the new scmi_sensor_proto_ops interface

Port the scmi iio driver to the new SCMI sensor interface based on
protocol handles and common devm_get_ops().

Link: https://lore.kernel.org/r/20210316124903.35011-26-cristian.marussi@arm.com
Link: https://lore.kernel.org/r/20210330134711.1962-1-cristian.marussi@arm.com


Acked-by: Jyoti Bhayana <jbhayana@google.com>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Tested-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>