Existing Open Firmware practice is to report each processor core as a
separate node in the device tree.  Report the value of the "reg" OF
property corresponding to a logical CPU's device node as the core_id
attribute in /sys/devices/system/cpu/cpu*/topology/core_id.
Signed-off-by: NNathan Lynch <ntl@pobox.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>