Revert "drm/amd/display: Set RMX_ASPECT as default"

This reverts commit 91b66c47.

Forcing RMX_ASPECT as default uses the preferred/native mode's timings
for any mode the user selects and scales the image. This provides a
a consistently nicer result in the case where the selected mode's
refresh rate matches the native mode's refresh but this isn't always
the case.

For example, if the monitor is 1080p@144Hz and the preferred mode is
60Hz then even if the user selects 1080p@144Hz as their selected mode
they'll get 1080p@60Hz.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>