Protect script when ram_freq is not set
Safely load PSCI DTO to enable CPUidle driver: psci_idle
The PSCI DTO shall only be applied if TF-A & Crust
support CPU idle states [0]. Otherwise the CPU usage
will be at 100%. This will not be visible in top,
lead to overheating and battery drain.
Worst case scenario would lead to a fried chip if
the CPU thermal_zone does not work or is not enabled
in DTS.
[0] https://gitlab.com/postmarketOS/pmaports/-/issues/1901#note_1238456920
