The root node of upstream RPI3 DTBs used to be compatible with brcm,brcm2836: it is not any longer. Therefore, add brcm,bcm2837 as a compatibility string to our platform and drivers.
For reference, from the device trees available at https://github.com/raspberrypi/firmware/blob/master/boot/:
compatible = "raspberrypi,3-model-b", "brcm,bcm2837"; model = "Raspberry Pi 3 Model B";
compatible = "raspberrypi,3-model-b-plus", "brcm,bcm2837"; model = "Raspberry Pi 3 Model B+";