drm/amdgpu: support dpm level modification under virtualization v3

Under vega10 virtualuzation, smu ip block will not be added.
Therefore, we need add pp clk query and force dpm level function
at amdgpu_virt_ops to support the feature.

v2: add get_pp_clk existence check and use kzalloc to allocate buf

v3: return -ENOMEM for allocation failure and correct the coding style

Signed-off-by: Yintian Tao <yttao@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>