drm/amdgpu: Dynamically initialize IP instance attributes

Dynamically initialize IP instance attributes. This eliminates bugs
stemming from adding new attributes to an IP instance.

Cc: Alex Deucher <Alexander.Deucher@amd.com>
Reported-by: Tom StDenis <tom.stdenis@amd.com>
Fixes: 4d7ba312 ("drm/amdgpu: Add "harvest" to IP discovery sysfs")
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
Acked-by: Alex Deucher <Alexander.Deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>