htc-m8: fix dt.img generation

Ever since the HTC One (M8) was added to postmarketOS, there was an issue with booting the generated image (see #63 (closed)). The discussion at the end had the solution, the dtbs need to be sorted using the custom property "htc,project-id". At that time, postmarketOS' dtbTool did not have the option to specify a custom sorting tag, but it gained it about 2 years ago with c6e30009.

Use that option so the dt.img is correctly generated.

Tested on my htc-m8.