drm/amdgpu: Pulling old prepare and submit for flip back

This is needed to ensure every single DC commit builds. Reverting
this again when it's no longer needed by DC.

This reverts commit 98da65d5.

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>