drm/amdgpu/pm: rework the hwmon visibility settings

Previously we just always exposed everything for asics
supported by powerplay.  Make it a bit more fine grained.
In practice this shouldn't change anything.

Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>