drm/amd/display: combine watermark change and clock change for update clocks.

[Why]
underflow happened when playing video on 1366x768 + 4K clone mode due to
incorrect handle watermark change flag and lower down clocks to early.

[How]
Check watermark change flag when decide doing optimized, and check
optimized required flag to do clock update.

Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Reviewed-by: Eric Yang <eric.yang2@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>