drm/amd/display: do not allocate display_mode_lib unnecessarily

This allocation isn't required and can fail when resuming from suspend.

Bug: https://gitlab.freedesktop.org/drm/amd/issues/1009


Signed-off-by: Dor Askayo <dor.askayo@gmail.com>
Reviewed-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>