ARM: dts: UniPhier: re-license device tree files under GPLv2+/X11

The current GPL only licensing on the device trees makes it very
impractical for other software components licensed under another
license.

To make it easier to reuse them, the device trees for UniPhier
SoCs and boards have already been dual-licensed in Linux.

Follow this trend in U-boot too.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>