drm/amd/powerplay: Add CG and PG support for tonga

Implement clock and power gating support for tonga.  On Tonga
this is handles by the SMU rather than direct register settings
in the driver.

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