gitattributes: Treat .bin files as binary.

Binary files, which are committed to a private fork of this repository,
will be subject to line feed substitution unless marked as binary.

Mark .bin files as binary.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

.gitattributes

 # Declare files that always have LF line endings on checkout
 * text eol=lf
 # Denote all files that are truly binary and should not be modified
+*.bin binary
 *.bmp binary
 *.ttf binary
 *.gz binary