I found a good solution. In the grub.d directory, edit the file 10_Linux. Search for the line with 'devicetree' (just one). Create a new directory named 'dtb' in the /boot directory and put in it your .dtb file. Now grub could find the dtb directory and load the devicetree just changing the pointer in the line containing 'devicetree'. Run sudo update-grub. That worked fine on my lenovo ideapad 5-2in1 laptop!