amdgpu/pm: Enable sysfs nodes for vclk and dclk for NAVI12

SMI clock measure API is failing on NAVI12, because
sysfs node for pp_dpm_vclk is not existing. Enable
sysfs node for pp_dpm_vclk for NAVI12.

v2: Also enable sysfs node for pp_dpm_dclk.

Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Marko Zekovic <Marko.Zekovic@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>