ARM: dts: imx: add common imx7ulp dtsi support

The i.MX 7ULP family of processors features NXP's advanced implementation
of the Arm Cortex-A7 core, the Arm Cortex-M4 core, as well as a 3D and 2D
Graphics Processing Units (GPUs).

This patch aims to add the initial support including:
1) CLK
2) GPIO PTC, PTD, PTE, PTF
3) uSDHC 1/2
4) LPUART 4/5/6/7
5) LPI2C 6/7

Cc: Rob Herring <robh+dt@kernel.org>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: devicetree@vger.kernel.org
Cc: Sascha Hauer <kernel@pengutronix.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>