drm/amdgpu: prepare DCE6 uniformisation with DCE8 and DCE10

Let's begin the cleanup in sid.h to prevent warnings and errors when wiring
sid.h into dce_v6_0.c.

This is a bigger cleanup.
Many defines found under sid.h have already been properly moved
into the different "_d.h" and "_sh_mask.h", so they should have been
already removed from sid.h and properly linked in where needed.

Signed-off-by: Alexandre Demers <alexandre.f.demers@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>