drm/amd/display: Destroy DC context while keeping DML and DML2

If there is memory pressure at suspend time then dynamically
allocating a large structure as part of DC suspend code will
fail.

Instead re-use the same structures and clear all members except
those that should be maintained.

Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2362


Acked-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>