drm/amd/pm: add get_dpm_ultimate_freq function for cyan skillfish
Some clients(e.g., kfd) query sclk/mclk through this function.
As cyan skillfish doesn't support dpm, for sclk, set min/max
to CYAN_SKILLFISH_SCLK_MIN/CYAN_SKILLFISH_SCLK_MAX(to maintain the
existing logic).For others, set both min and max to current value.