drm/amd: Add concept of running prepare_suspend() sequence for IP blocks

If any IP blocks allocate memory during their hw_fini() sequence
this can cause the suspend to fail under memory pressure.  Introduce
a new phase that IP blocks can use to allocate memory before suspend
starts so that it can potentially be evicted into swap instead.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>