drm/amd/pm: modify the fine grain tuning function for vangogh

This patch is to modify the fine grain tuning function for vangogh.
This patch uses the existing old flag to make the two sysfs files
work separately -- "power_dpm_force_performance_level" and
"pp_od_clk_voltage".
Only the power_dpm_force_performance_level is switched to "manual"
mode, the fine grain tuning function will be started.
In other mode, including "high","low","min_sclk","min_mclk",
"standard" and "peak", the fine grain tuning function will be shut down,
and the frequency range of gfx and cpu clock will be restored the
default values.

Signed-off-by: Xiaojian Du <Xiaojian.Du@amd.com>
Reviewed-by: Kevin Wang <kevin1.wang@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>