fdt: Report the devicetree source

It can be confusing to figure out where the devicetree came from. It seems
important enough to warrant a message during boot. Add information about
the number of devices and uclasses too since it is helpful to have some
idea what is going on with driver model.

Report the devicetree source in bdinfo too.

This looks something like this, with > marking the new line.

   U-Boot 2021.10-00190 (Oct 30 2021 - 09:01:29 -0600)

   DRAM:  128 MiB
>  Core:  42 devices, 11 uclasses, devicetree: passage
   Flash: 64 MiB

Signed-off-by: Simon Glass <sjg@chromium.org>