drm/amd/display: Limit display scaling to up to 4k for DCN 3.1

[why]
The existing limit was mistakenly bigger than 4k for DCN 3.1

Reviewed-by: Zhan Liu <Zhan.Liu@amd.com>
Acked-by: Solomon Chiu <solomon.chiu@amd.com>
Signed-off-by: Nikola Cornij <nikola.cornij@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org