Enable SPI1 bus on Debian?

I’ve tried to interpret the available info out there, but I haven’t gotten it to work: I need to enable SPI bus 1 (pins P9 28-31) on the latest Debian. In short, what is the current, up-to-date recommended way to install a .dtbo at runtime, and what’s the recommended .dtbo for SPI1? Or is there some even newer to do it now? Also, will I have to disable HDMI for this to work?

Strange…I swear I had it working for a moment using Hipster’s BB-SPI1-01 overlay (http://hipstercircuits.com/category/device-tree/), enabled that with Capemgr. Then I enabled UART1 as well, and it stopped working, and I can’t get it working anymore.