drm/amd/display: limit the v_startup workaround to ASICs older than DCN3.1

Since, calling dcn20_adjust_freesync_v_startup() on DCN3.1+ ASICs
can cause the display to flicker and underflow to occur, we shouldn't
call it for them. So, ensure that the DCN version is less than
DCN_VERSION_3_1 before calling dcn20_adjust_freesync_v_startup().

Cc: stable@vger.kernel.org
Reviewed-by: Fangzhi Zuo <jerry.zuo@amd.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>