In theory, any platform that supports CPU_SUSPEND would be able to support both platform-coordinated mode and OS-initiated mode, since the power state coordination happens either in the PSCI library implementation or in an HLOS.
Just to highlight, it is just the coordination that happens in PSCI/EL3 or HLOS.
It just adds extra implementation in the kernel and hence the execution path and
doesn't simplify anything in the firmware. Firmware complexity will be the same for both
PC and OSI and he needs to deal with all the races even if HLOS takes care of last
man in and first man out *in its view* .