firmware: arm_scmi: Add protocol modularization support

Extend SCMI protocols accounting mechanism to address possible module
usage and add the support to possibly define new protocols as loadable
modules.

Keep the standard protocols built into the SCMI core.

Link: https://lore.kernel.org/r/20210316124903.35011-38-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>