init: /dev can be noexec and /run nodev

/dev used to be mounted with "exec" flag due to /dev/MAKEDEV script
but that's history and it's now located in /sbin. mmap() with file
descriptor to "/dev/zero" (instead of modern mmap(,,,MAP_ANON...))
will still work.

There's no reason to have (char/block) device nodes in /run, so let's
mount it with "nodev". This does not affect sockets, fifos etc.

Signed-off-by: Topi Miettinen <toiwoton@gmail.com>