firmware: arm_scmi: Add SCMI device for system power protocol

Add SCMI device for system power protocol by just adding the name "syspower"
to the list of supported core protocol devices.

Link: https://lore.kernel.org/r/20200907174657.32466-3-cristian.marussi@arm.com


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