arm64: dts: imx8ulp: Add the basic dtsi file for imx8ulp

Add the basic dtsi support for i.MX8ULP.

i.MX 8ULP is part of the ULP family with emphasis on extreme
low-power techniques using the 28 nm fully depleted silicon on
insulator process. Like i.MX 7ULP, i.MX 8ULP continues to be
based on asymmetric architecture, however will add a third DSP
domain for advanced voice/audio capability and a Graphics domain
where it is possible to access graphics resources from the
application side or the realtime side.

Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Jacky Bai <ping.bai@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>