drm/amdgpu: Set DPM_FLAG_NEVER_SKIP when enabling PM-runtime

commit d33158530660bc89be3cc870a2152e4e9a76cac7 upstream.

Based on a similar patch from Rafael for radeon.

When using ATPX to control dGPU power, the state is not retained
across suspend and resume cycles by default.  This can probably
be loosened for Hybrid Graphics (_PR3) laptops where I think the
state is properly retained.

Fixes: c62ec461 ("PM / core: Fix direct_complete handling for devices with no callbacks")
Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>