drm/amdgpu: rename amdgpu_dpm_funcs to amd_pm_funcs

renamed amdgpu_dpm_funcs and moved to amd_shared.h
so can shared with powerplay.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>