Platform/Sgi: Low Power Idle States for RD-Fremont

RD-Fremont platform supports two LPI states, LPI1 (Standby WFI) and LPI3
(Power-down). The cluster supports LPI2 (Power-down) state. The LPI
implementation also supports combined power state for core and cluster.

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