drm/amd/display: Don't stretch non-native images by default in eDP

commit 978fa2f ("drm/amd/display: Use scaling for non-native
resolutions on eDP") started using the GPU scaler hardware to scale
when a non-native resolution was picked on eDP. This scaling was done
to fill the screen instead of maintain aspect ratio.

The idea was supposed to be that if a different scaling behavior is
preferred then the compositor would request it.  The not following
aspect ratio behavior however isn't desirable, so adjust it to follow
aspect ratio and still try to fill screen.

Note: This will lead to black bars in some cases for non-native
resolutions. Compositors can request the previous behavior if desired.

Fixes: 978fa2f ("drm/amd/display: Use scaling for non-native resolutions on eDP")
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4538
Signed-off-by: Mario Limonciello (AMD) <[email protected]>
Acked-by: Alex Deucher <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>
(cherry picked from commit 825df7f)

Author: superm1

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -8030,7 +8030,7 @@ static int dm_encoder_helper_atomic_check(struct drm_encoder *encoder,
 				       "mode %dx%d@%dHz is not native, enabling scaling\n",
 				       adjusted_mode->hdisplay, adjusted_mode->vdisplay,
 				       drm_mode_vrefresh(adjusted_mode));
-			dm_new_connector_state->scaling = RMX_FULL;
+			dm_new_connector_state->scaling = RMX_ASPECT;
 		}
 		return 0;
 	}