ext: nffs: Pull in Apache Mynewt NFFS implementation

Origin: Apache Mynewt NFFS
URL: https://github.com/apache/mynewt-nffs/tree/master
Commit: 6639f7a432e70db00ef25d5e558aedbe503a3c9a
Purpose: Introduction of NFFS (Newtron Flash File System)
Maintained-by: External

Signed-off-by: Andrzej Kaczmarek <andrzej.kaczmarek@codecoup.pl>
27 files changed