ACPI / scan: Add acpi_device objects for all device nodes in the namespace

Modify the ACPI namespace scanning code to register a struct
acpi_device object for every namespace node representing a device,
processor and so on, even if the device represented by that namespace
node is reported to be not present and not functional by _STA.

There are multiple reasons to do that.  First of all, it avoids
quite a lot of overhead when struct acpi_device objects are
deleted every time acpi_bus_trim() is run and then added again
by a subsequent acpi_bus_scan() for the same scope, although the
namespace objects they correspond to stay in memory all the time
(which always is the case on a vast majority of systems).

Second, it will allow user space to see that there are namespace
nodes representing devices that are not present at the moment and may
be added to the system.  It will also allow user space to evaluate
_SUN for those nodes to check what physical slots the "missing"
devices may be put into and it will make ...