MIPS: Lantiq: Move device-trees to arch/mips/boot/dts/

Move the Lantiq device-trees to arch/mips/boot/dts/ and update the
Makefiles accordingly.  There is currently only a single Lantiq
device-tree (EASY50712), and it's required to be built into the kernel,
so select BUILTIN_DTB for it.

Signed-off-by: Andrew Bresticker <abrestic@chromium.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Cc: Kumar Gala <galak@codeaurora.org>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Paul Burton <paul.burton@imgtec.com>
Cc: David Daney <david.daney@cavium.com>
Cc: John Crispin <blogic@openwrt.org>
Cc: Jayachandran C <jchandra@broadcom.com>
Cc: Qais Yousef <qais.yousef@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Cc: devicetree@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/7559/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>