fs/cpio: don't extend packages' permissions table

Currently, when we build a cpio filesystem without static devices, we
shoehorn the /dev/console node as if it were specified by a package.

This means that this device is added for all filesystems as well, not
just the cpio. But if we disable cpio, that device is not created for
other filesystems.

This is not very clean, and may break expectations.

Instead, use an explicit mknod as part of the _CMD, as we know it's
going to run under fakeroot.

This is still visible to all filesystems built after cpio, and not to
those built before it, though.

[Peter: ensure /dev exists, simplify comment]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>