retroarch: add core info files to configuration

[cmitu]

Core info files are needed starting from 1.10.1 in order to enable save/load state, rewind, runahead, (disk control ?).
In addition to that, they're needed for netplay clients to work (see issue #3161).

NOTE: this PR and #3548 should fix issue #3161.

[cmitu]

Adding the info files will enable the start-up info to pop-up:

If we don't want that, I can add the retroarch.cfg parameter to disable it, should be easy to find (tm).

[joolswills]

I'm not sure. It may be best to disable it by default to keep current behaviour.

[cmitu]

@joolswills ok, added the config option to quiesce the info blurb.

I also checked the libretro cores that we ship and the upstream repository is missing a few .info files:

• mess and mess2016. We can clone them based on mame and mame2016.
• superflappybirds. No idea what are the capabilities, I'll have to give it a spin.
• mupen64plus. We can clone it from mupen64plus-next.

My idea for the missing core info files is to generate them from the scriptmodule, via configure, instead of adding them in retroarch. Apart from the mupen64plus core, they're not installed by default.

[joolswills]

Thanks.