package/dtc: fix license hashes

Update hash of license files and add BSD-2-Clause file, see
https://git.kernel.org/pub/scm/utils/dtc/dtc.git/commit/?id=25bb080c18d1a8a96760e26257bf8c80ec7fcab4
https://git.kernel.org/pub/scm/utils/dtc/dtc.git/commit/?id=702c1b6c0e73d2bcf24f0b8398aca6a940863e48

Fixes:
 - http://autobuild.buildroot.org/results/d3db8ddc096f09bb1728a0ba40b925fbf49c424b



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>