amd/powerplay: fix the issue of uclk dpm

PPSMC_MSG_SetUclkFastSwitch message can be applied on vega20,
but can't on navi10. This is the prerequisite of uclk dpm on
navi10.

Signed-off-by: Kenneth Feng <kenneth.feng@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>