Commit 0ceace927c4c ("Xilinx FPGAs: Eliminate Vivado critical
warnings", 2024-03-08) incorrectly removed the constraints for
shield_io36 through to shield_io44 (due to me applying the wrong
version of a patch), resulting in Vivado giving compile errors when
building for the Arty A7. This restores the constraints.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>