Integrate meta-seconorth-machine/add_nxp_override

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Commit: seco-ne/yocto/layers/meta-seconorth-machine@0f380b0a

machines: Add new seco-nxp machine override

We need an additional override that has a higher prio than the ones from
meta-freescale but still can be overridden by specific machine overrides
(e.g. seco-mx8mp).
The override is intended for vendor specific config files (e.g.
weston.ini).