Unlike Linux, barebox has a build-time dependency on the fdtget utility.
For this reason, we can't import the kernel dtc Makefile by mere
copying. Reinstate the fdtget-specific bits that got lost in the
last dtc update. This fixes barebox imd generation which has caused
following error message in master:

	gen-dtb-s: line 37: scripts/dtc/fdtget: No such file or directory

Fixes: 4e731e48d4 ("scripts/dtc: Update to upstream version v1.5.0")
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>