firmware: arm_scmi: Generalize the fast channel support

Generalize existing fast channel support used in the perf protocol and
make it available to possibly any protocol refactoring the common code
into a couple of new scmi_proto_helpers_ops routines.

Make perf protocol use this new infrastructure.

No functional change.

Link: https://lore.kernel.org/r/20220704102241.2988447-4-cristian.marussi@arm.com


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