I've reversed those files in the past as well, and you're correct, they are TrustZone applications (like Widevine, DxDHCP, Keymaster and more). I have a script which can be used to reunite these pieces of code into an ELF file which can be loaded into IDA (more about this in about a month!)

Anyway, if you're looking to load arbitrary code into TZ, wait for the next blog post (approx. 2-3 days)!