I am using VSCode with SDK 2.9.1. I have added the spi21 to the device tree UI editor. When I choose the MOSI, MISO and SCLK, they all show up in the visual representation to the right. When I choose a pin for CS, a new line appears and the pin in the visual representation doesn't show what I chose.
Here you can see what I mean:
Notice that the spi0 that was already defined the CS shows up fine. This may just be a visual error, but I wanted to report it in case it mattered.