drm/amd/display: Refactor atomic commit implementation. (v2)

Modify amdgpu_dm_atomic_comit to implement
atomic_comit_tail hook.
Unify Buffer objects allocation and dealocation
for surface updates and page flips.
Simplify wait for fences and target_vbank logic
for non blockiing commit.
Remove hacky update surface to page flip synchronization
we had and rely on atomic framework synchronization logic.

v2:
Add state->allow_modeset as indicator of page flip call.

Signed-off-by: Andrey Grodzovsky <Andrey.Grodzovsky@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>