drm/amd/powerplay: support retrieving clock information from other sysplls

There will be some needs to retrieve clock information from other
sysplls also except default 0.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>