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

These are build artifacts, which should be ignored by git.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Greentime Hu <greentime@andestech.com>
Signed-off-by: Greentime Hu <greentime@andestech.com>