drm/amd/display: Fix overlapping copy within dml_core_mode_programming

[WHY]
&mode_lib->mp.Watermark and &locals->Watermark are
the same address. memcpy may lead to unexpected behavior.

[HOW]
memmove should be used.

Reviewed-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Acked-by: Wayne Lin <wayne.lin@amd.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Hersen Wu <hersenxs.wu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>