ARM: dts: berlin: relicense the BG2CD Google Chromecast dts under GPLv2/X11

The current GPLv2 only licensing on this dts makes it very impractical
for other software components licensed under another license.

In order to make it easier for them to reuse our device trees, relicense
this dts under a GPLv2/X11 dual-license.

Signed-off-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>