[File] Detect YAFFS images

[Fabian Zaremba]

* FC Stegerman (24.01.23 17:45):
> I wrote (and attached) a v3 patch that only recognises valid enums ��
> 
> NB: if you decide to use it, please test it, since I did not.

Thank you very much for improving the signature :)

I tested it successfully - this signature correctly recognizes all 
generated test cases as well as the YAFFS image extracted from a Google 
device NAND dump.

@Christos: Could you please evaluate inclusion of this version into the 
magic data shipped with file?

Thanks for your efforts!

Best regards,
Fabian