ARM: dts: imx6: add DT for aristainetos2 board

This patch adds support for the imx6dl based aristainetos2 board
with following configuration:

CPU:   Freescale i.MX6DL rev1.1 at 792 MHz
MReset cause: POR
MBoard: aristaitenos2
DRAM:  1 GiB
NAND:  1024 MiB
MMC:   FSL_SDHC: 0, FSL_SDHC: 1
SF: Detected N25Q128A with page size 256 Bytes, erase size 64 KiB, total 16 MiB
Display: lb07wv8 (800x480)

As this board can be used with 2 different display types, the
differences between them are extracted into 2 DTS files, and
the common settings are collected in a common file.

Signed-off-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>