arm64: dts: imx8qxp: Add lpuart1/lpuart2/lpuart3 nodes

lpuart nodes are part of the ADMA subsystem. See Audio DMA
memory map in iMX8 QXP RM [1]

This patch is based on the dtsi file initially submitted by
Teo Hall in i.MX NXP internal tree.

[1] https://www.nxp.com/docs/en/reference-manual/IMX8DQXPRM.pdf



Signed-off-by: Teo Hall <teo.hall@nxp.com>
Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>
Reviewed-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>