I have constrained DCI_CASCADE in Vivado Design Suite.
Is it possible to confirm that it has been implemented?
1) Open the implemented design
2) In Package View select the bank to which you have applied the DCI_CASCADE property and check its properties.
3) This will show you all of the properties applied on that particular bank, including DCI_CASCADE.
You can also use the below Tcl command in open implemented design:
report_property [get_iobanks 14]
This will give you all of the properties on BANK 14.
The same command can also be used for other Banks.