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.

Before this patch:
 # /opt/rocm/opencl/bin/clinfo

 Max clock frequency:                           0Mhz

After this patch:
 # /opt/rocm/opencl/bin/clinfo

 Max clock frequency:                           2000Mhz

v2:
 - Maintain the existing min/max sclk logic.(Lijo)
v3:
 - Avoid fetching metrics table twice.(Lijo)

Signed-off-by: Lang Yu <Lang.Yu@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>