Handling of __fixups__ and __local_fixups__ removes precious data

[ukleinek]

This commit uncovers a problem that we already have since commit 915daad ("Start with empty local_fixups and fixups nodes"):

$ cat test.dts 
/dts-v1/;
/plugin/;

/ {
	node {
		property = <0xffffffff>, "string";
	};
	
	__fixups__ {
		somenode = "/node:property:0";
	};
};

$ dtc -I dts -O dts test.dts 
/dts-v1/;

/ {

	node {
		property = <0xffffffff>, "string";
	};
};

Originally posted by @ukleinek in #151 (comment)

[ukleinek]

FTR, this is addressed in https://lore.kernel.org/devicetree-compiler/20250801160031.624886-2-u.kleine-koenig@baylibre.com