drm/amd/display: Ensure DCN save after VM setup

[Why]
DM initializes VM context after DMCUB initialization.
This results in loss of DCN_VM_CONTEXT registers after z10.

[How]
Notify DMCUB when VM setup is complete, and have DMCUB
save init registers.

v2: squash in CONFIG_DRM_AMD_DC_DCN3_1 fix

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Jake Wang <haonan.wang2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>