feat(plat/sgi): enable AMU for RD-V1-MC
feat(plat/sgi): enable AMU for RD-V1-MC

AMU counters are used for monitoring the CPU performance. RD-V1-MC
platform has architected AMU available for each core. Enable the use of
AMU by non-secure OS for supporting the use of counters for processor
performance control (ACPI CPPC).

Change-Id: I33be594cee669e7f4031e5e5a371eec7c7451030
Signed-off-by: Pranav Madhu <83076119f14107711984183f43407dcaaec02e85@arm.com>

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware