fs: set packages permissions even with no system device tables

fs: set packages permissions even with no system device tables

Currently, when there is no syztem device table (permissions or static
devices) defined, then package permissions are not applied, because they
are guarded by the check on the system device tables being non empty.

Fix that by narrowing the guarding condition.

Note that the dependency on host-makedevs was not conditional; we always
build it even if we don't need it. Making it conditional is not
possible, because we don't know all the packages permissions by the time
the fs infra is parsed (packages from br2-external are parsed after it).

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>