scripts/dtc: import update-dtc-source.sh from kernel v4.0-rc1
The original script was written by Grant Likely <grant.likely@linaro.org>.
The version for barebox also imports some libfdt sources, so that we are
able to compile the fdtget host tool. Also remove the unused non-kconfig
makefiles.
Signed-off-by: Jan Luebbe <jlu@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>