drm/amd/display: Require minimum VBlank size for stutter optimization

If the nominal VBlank is too small, optimizing for stutter can cause
the prefetch bandwidth to increase drasticaly, resulting in higher
clock and power requirements. Only optimize if it is >3x the stutter
latency.

Reviewed-by: Austin Zheng <austin.zheng@amd.com>
Signed-off-by: Dillon Varone <dillon.varone@amd.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>