ACPI / hotplug / PCI: Consolidate acpiphp_enumerate_slots()

The acpiphp_enumerate_slots() function is now split into two parts,
acpiphp_enumerate_slots() proper and init_bridge_misc() which is
only called by the former.  If these functions are combined,
it is possible to make the code easier to follow and to clean up
the error handling (to prevent memory leaks on error from
happening in particular), so do that.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>