drm/amd/display: Limit Minimum FreeSync Refresh Rate

Why:
Some EDIDs report a minimum refresh rate lower than what HW can support

How:
Add a check to calculate minimum supported refresh rate with current timing
and use that as the minimum if a lower one is passed in

Acked-by: Stylon Wang <stylon.wang@amd.com>
Signed-off-by: Austin Zheng <austin.zheng@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>