sparc: gitignore a few files

With this 'git status' no longer reports any new files
At least not for a sparc allnoconfig build
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

arch/sparc/boot/.gitignore

+btfix.S
+btfixupprep
+image
+zImage
+

arch/sparc/kernel/.gitignore

+vmlinux.lds