drm/amd/display: Add disable triple buffering DC debug option

Added a "disable_tri_buf" DC debug option. When set to 1  feature will
be off.

Signed-off-by: Charlene Liu <charlene.liu@amd.com>
Reviewed-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>