How to add Intel IP to Custom IP (hw.tcl)?

Nope, it is not an example to add .v or .sv files.

If you refer to https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/ug/ug-qpp-platform-designer.pdf page 122 example 18.

it shows you an example of how to add an Emif instance using the IP. This include on how you should create it in the .v and the hw.tcl.

with this example, you can use it for the altclkctrl as specified in your above.