hexagon: ignore vmlinux.lds

After building allmodconfig, there is an untracked vmlinux.lds file in
arch/hexagon/kernel:

$ git ls-files . --exclude-standard --others
arch/hexagon/kernel/vmlinux.lds

Ignore it as all other architectures have.

Link: https://lkml.kernel.org/r/20211115174250.1994179-4-nathan@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Cc: Brian Cain <bcain@codeaurora.org>
Cc: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>