drm/amd/pm: correct the usage for 'supported' member of smu_feature structure

The supported features should be retrieved just after EnableAllDpmFeatures message
complete. And the check(whether some dpm feature is supported) is only needed when we
decide to enable or disable it.

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