nds32: add vmlinux.lds and vdso.so to .gitignore

These are build artifacts, which should be ignored by git.
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: NGreentime Hu <greentime@andestech.com>
Signed-off-by: NGreentime Hu <greentime@andestech.com>

arch/nds32/kernel/.gitignore

+vmlinux.lds

arch/nds32/kernel/vdso/.gitignore

+vdso.lds