Platform/Sgi: Add CPPC support for RD-Fremont platform

Enable ACPI CPPC mechanism for RD-Fremont as defined by the ACPI
specification. The implementation uses AMU registers accessible as
Fixed-feature Hardware (FFixedHW) for monitoring the performance.
Non-secure SCMI fastchannels are used to communicate with LCP to set the
desired performance. In addition to this, RD-Fremont platform does not
support CPPC revision 1 and below. So update the _OSC method to let OSPM
know about this fact.

Signed-off-by: Prabin CA <prabin.ca@arm.com>