These are memory initialization files that can be used by the Pretty Secure Processor.
font.mem is an encoded version of Adobe Font's Open-Source "Source Code Pro" font converted with img2v.py.
splashscreen.mem is an initializer file for text-mode RAM that contains a popup box saying "Pretty Secure Processor"
logo.mem is the Pretty Secure Processor logo encoded as a 120 by 120 image, ready to be used as a hardware sprite.
To use these files in Vivado, add them as simulation sources and they can be included with $readmemh directly (no absolute path required!)