Add acpi_resource_consumer().  This takes a struct resource and searches
the ACPI namespace for a device whose current resource settings (_CRS)
includes the resource.  It returns the device if it exists, or NULL if no
device uses the resource.

If more than one device uses the resource (this may happen in the case of
bridges), acpi_resource_consumer() returns the first one found by
acpi_get_devices() in its modified depth-first walk of the namespace.
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>