drm/amd: avoid suspend on dGPUs w/ s2idle support when runtime PM enabled

dGPUs connected to Intel systems configured for suspend to idle
will not have the power rails cut at suspend and resetting the GPU
may lead to problematic behaviors.

Fixes: e25443d2

 ("drm/amdgpu: add a dev_pm_ops prepare callback (v2)")
Link: https://gitlab.freedesktop.org/drm/amd/-/issues/1879
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>