drm/amd/pm: early return if disabling DPMS for GFX IP v11.5.2

This was intended to add support for GFX IP v11.5.2, but it needs
to be applied to all GFX11 and subsequent APUs. Therefore the code
should be revised to accommodate this.

Signed-off-by: Tim Huang <tim.huang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>