firmware: arm_scmi: Populate a common SCMI debugfs root

firmware: arm_scmi: Populate a common SCMI debugfs root

Create a common SCMI debugfs root directory and populate it with some
common SCMI data for each discovered SCMI platform instance if SCMI
debugfs is needed by any configured SCMI facility.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>
Tested-by: Florian Fainelli <f.fainelli@gmail.com>
Tested-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lore.kernel.org/r/20230118121426.492864-11-cristian.marussi@arm.com
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>