Generate roms dirs and es_systems.cfg automatically

[substring]

Please make sure your PR is ready to be merged !

• You added the changes in CHANGELOG.md
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Fixes #XXXX

Changes :

• new packages branch : package/recalbox-roms
• this package branch has 1 package per system
• emulators' Config.in select the recalbox-romfs- to trigger the making of the roms folder + es_input.cfg entries
• share_init/roms is no longer needed
• no impact on defconfigs as it all relies on dependencies
• added scripts/linux/empack.py that helps building a system recalbox-romfs package. It will be documented
• all recalbox-romfs- have been nuilt using empack, the command-line used to build the makefile is mentionned in each .mk
• add add libxml2-utils tto validate XML generated by recalbox-romfs

Related to (put here the others PR in other repositories)

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Wrote a wiki on how to use empack.py : https://github.com/recalbox/recalbox-os/wiki/Recalbox-development-add-emulator-filesystem-(EN)

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@digitalLumberjack Build ok on #6027156
Couldn't test all emulators/cores, but so far the es_system.cfg is fine for a pi3, and doesn't embed cores that are not compiled on pi (wii, gamecude ...). X86_64 specific systems do show for this arch. Time to review :)

[digitalLumberjack]

Cannot we define a function in a parent package and call it with specific emulator options to create the xml ?

[substring]

I'm not sure we can pass arguments to such a function. Anyway, there is the distinction between emulators and cores. I don't know about any "define" function that can also return what you expect

[LipkeGu]

Cannot we define a function in a parent package and call it with specific emulator options to create the > xml ?

You could get this job (create directories) done via ES itself... let ES scan the xml and let it create the directories based on the platform. the xml file is done via Makefiles or python scripts...

<systemList>
<system>
<name>snes</name>
<fullname>Super Nintendo Entertainment System</fullname>
<path>~/roms/snes</path> <---- let ES create this path.
<extension>.smc .sfc .SMC .SFC</extension>
<command>snesemulator %ROM%</command>
<platform>snes</platform>
<theme>snes</theme>
</system>
</systemList>

[substring]

The PR is ALSO about generating es_systems.cfg. that's the hardest part