drm/amd/display: Don't re-program planes for DPMS changes

[Why]
There are opt1c lock warnings and CRTC read timeouts when running the
"igt@kms_plane@plane-position-hole-dpms-pipe-*" tests. These are
caused by trying to reprogram planes that are not in the current
context.

DPMS off removes the stream from the context. In this case:

new_crtc_state->active_changed = true
new_crtc_state->mode_changed = false

The planes are reprogrammed before the stream is removed from the
context because stream_state->mode_changed = false.

For DPMS adds the stream and planes back to the context:

new_crtc_state->active_changed = true
new_crtc_state->mode_changed = false

The planes are also reprogrammed here before the stream is added to the
context because stream_state->mode_changed = true. They were not
previously in the current context so warnings occur here.

[How]
Set stream_state->mode_changed = true when
new_crtc_state->active_changed = true too.

This prevents reprogramming before the context is applied in DC. The
programming will be done after the context is applied.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Sun peng Li <Sunpeng.Li@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Acked-by: Tony Cheng <Tony.Cheng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>