Update .gitignore for arch/i386/boot

With the new setup code, we generate a couple more files

Signed-off-by: Matthew Wilcox <matthew@wil.cx>
[ .. and do the same for x86-64 - Alexey ]
Acked-by: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>