testing/*apq8026-smartwatches*: add mainline dtb reference

asus-sparrow and lg-lenok have been upstream in Linux for a bit, huawei-sturgeon is on the list and is not expected to change the dtb name.

Add the reference to the deviceinfo files, and while it's not used by postmarketOS at this time, it is being used by my tooling for mainline kernel building.

I'm probably going to submit 8226 mainline kernel into pmaports also in the not-so-distant future.