config.boot.commandLineDtbNode can be set from `bootargs` to
`bootargs-override` (used for boards where the u-boot on the board does
set `bootargs` on its own).
In that case, the code updating the cmdline for tftpboot purposes also
needs to update this node, not the `bootargs` node.
Otherwise the kernel won't find the phram device, as it never heard
about it, as it didn't get the necessary cmdline options.
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