ARM: dts: imx6qdl-dhcom: Split SoC-independent parts of DHCOM SOM and PDK2

ARM: dts: imx6qdl-dhcom: Split SoC-independent parts of DHCOM SOM and PDK2

The DH electronics PDK2 can be populated with SoM with i.MX6S/DL/D/Q
variants. Split the SoC-independent parts of the SoM and PDK2 into the
imx6qdl-dhcom-*.dtsi and reduce imx6q-dhcom-pdk2.dts to example of
adding i.MX6S/DL/D/Q variants of the SoM into a PDK2 carrier board.

Signed-off-by: Christoph Niedermaier <cniedermaier@dh-electronics.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Fabio Estevam <festevam@denx.de>
Cc: Marek Vasut <marex@denx.de>
Cc: NXP Linux Team <linux-imx@nxp.com>
Cc: kernel@dh-electronics.com
To: linux-arm-kernel@lists.infradead.org
Signed-off-by: Shawn Guo <shawnguo@kernel.org>