Rework the device trees of the OPOS6UL and OPOS6ULDev boards to support
the OPOS6UL SoM with an i.MX6ULL SoC.  The device trees are now as
following:

- imx6ul-imx6ull-opos6ul.dtsi
  common for both i.MX6UL and i.MX6ULL OPOS6UL SoM.
- imx6ul-opos6ul.dtsi
  for i.MX6UL OPOS6UL SoM. It includes imx6ul.dtsi and
  imx6ul-imx6ull-opos6ul.dtsi.
- imx6ull-opos6ul.dtsi
  for i.MX6ULL OPOS6UL SoM. It includes imx6ull.dtsi and
  imx6ul-imx6ull-opos6ul.dtsi.

- imx6ul-imx6ull-opos6uldev.dtsi
  OPOS6ULDev base device tree.
- imx6ul-opos6uldev.dts
  OPOS6ULDev board with an i.MX6UL OPOS6UL SoM. It includes
  imx6ul-opos6ul.dtsi and imx6ul-imx6ull-opos6uldevdtsi.
- imx6ull-opos6uldev.dts
  OPOS6ULDev board with an i.MX6ULL OPOS6UL SoM. It includes
  imx6ull-opos6ul.dtsi and imx6ul-imx6ull-opos6uldevdtsi.
Signed-off-by: Sébastien Szymanski <sebastien.szymanski@armadeus.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>