Expose CPU clock speed limits in PM firmware

[badly-drawn-wizards]

Following the discussion in this issue: https://gitlab.freedesktop.org/drm/amd/-/issues/2638

The amdgpu drivers for vangogh currently hard code the maximum clock frequency. If a steam deck is overclocked, then the AMD PowerPlay interface can only be set up to this hard coded limit, rather than the true maximum clock.

Steps to reproduce:

• Install PowerTools on an overclocked Steam Deck
• Set the pt_oc.json in the PowerTools configuration to match the current max clock
• Attempt to set the frequency above stock
• The kernel will log that the powerplay interface cannot be set beyond the stock max clock

Alternatively on a steam deck you can directly use the PowerPlay interface through the linux sysfs and the same will occur.

I am not familiar with the full details so I apologize if I haven't got the precise blocker for amdgpu on this side.