firmware: arm_scmi: Port genpd driver to the new scmi_power_proto_ops interface

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

Link: https://lore.kernel.org/r/20210316124903.35011-16-cristian.marussi@arm.com


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>