Unignore vmlinux.lds.h from Git.

Added !vmlinux.lds.h to .gitignore because it would otherwise be ignored.

Signed-off-by: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>