scmi_perf: Move protocol ops to separate file

This will allow conditional inclusion of SCMI Performance
commands operations.
That way we can choose to have only the core Perf and FastChannels
without the commands ops (for ACPI-based systems).

Unit test updated accordingly.

Change-Id: Ic2b915cdda46036b6431cca9cb44ea1960fbd28e
Signed-off-by: Nicola Mazzucato <nicola.mazzucato@arm.com>