dts: edtlib: Turn Node.instance_no into more flexible EDT.compat2nodes

[ulfalizer]

Add a dictionary EDT.compat2nodes that maps each compatible that appears
on some enabled node to a list of enabled nodes that implement the
compatible. For example, EDT.compat2nodes["foo"] is a list of all
enabled nodes whose 'compatible' includes "foo".

The old Node.instance_no functionality can easily be implemented in
terms of EDT.compat2nodes, so get rid of Node.instance_no.
EDT.compat2nodes is more powerful and easier to understand.

Simplify main() in gen_defines.py a bit by using EDT.compat2nodes to
generate the DT_COMPAT_ existence macros. The behavior is
slightly different now, as DT_COMPAT_ is generated for
enabled nodes that don't have a binding as well, but that might be an
improvement overall, and probably doesn't hurt.

EDT.compat2nodes will make the implementation of the new
$(dt_compat_get_str) preprocessor function in
#21560 cleaner and
simpler. That was the original motivation.

[ulfalizer]

CC @nandojve

[ulfalizer]

Bit arbitrary that EDT.compat2nodes only includes enabled nodes, though it's the only thing that's needed at the moment. I based it on Node.instance_no.

[nandojve]

Nice! This is a missing common point for gen_defines.py and Kconfig.
I already tested and for me it's ok.

Now it will be nice to have a dt_compat_count at gen_defines.py with the total instances to start replace things like that on drivers:

#if DT_INST_0_<compatible>
...
#endif
#if DT_INST_1_<compatible>
...
#endif
#if DT_INST_N_<compatible>
...
#endif

to

#if DT_<compatible>_COUNT > 0
REPEAT(DT_<compatible>_COUNT)
#endif

It's just a dream!

[zephyrbot]

All checks passed.

checkpatch (informational only, not a failure)

-:169: WARNING:UNDOCUMENTED_DT_STRING: DT compatible string "compat2nodes" appears un-documented -- check ./dts/bindings/
#169: FILE: scripts/dts/test.dts:303:
+			compatible = "compat2nodes";

-:173: WARNING:UNDOCUMENTED_DT_STRING: DT compatible string "compat2nodes" appears un-documented -- check ./dts/bindings/
#173: FILE: scripts/dts/test.dts:307:
+			compatible = "compat2nodes";

-:177: WARNING:UNDOCUMENTED_DT_STRING: DT compatible string "compat2nodes" appears un-documented -- check ./dts/bindings/
#177: FILE: scripts/dts/test.dts:311:
+			compatible = "compat2nodes";

-:183: WARNING:UNDOCUMENTED_DT_STRING: DT compatible string "compat2nodes-disabled" appears un-documented -- check ./dts/bindings/
#183: FILE: scripts/dts/test.dts:317:
+			compatible = "compat2nodes-disabled";

- total: 0 errors, 4 warnings, 187 lines checked

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[ulfalizer]

Rebased and improved version: #22250