drm/amd: Hide unsupported power attributes

Some ASICS only offer one type of power attribute, so in the visible
callback check whether the attributes are supported and hide if not
supported.

Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>