drm/amd/display: Update tmz_surface type to match register

[WHAT]
Update tmz_surface's type to match register size

Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Signed-off-by: Dmytro Laktyushkin <dmytro.laktyushkin@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>