update dontdiff file

Updates based on recent .gitignore updates:

*.o.*: Says Alexey Dobriyan:
These are presumably temporary gcc files, which aren't interesting.

setup.bin, setup.elf: new x86 boot code files (from Matthew Wilcox)

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>