[POWERPC] spu_manage: fix spu_unit_number for celleb device tree

This fixes a regression introduced with 2.6.23-rc4 after on some
confusion about the device tree interfaces.

IBM QS21 device trees provide "physical-id", so we changed the code to
run on that and remain compatible with all IBM machines.

However, the Toshiba Celleb device tree provides the "unit-id" property,
which was in the Linux code, but never used in this way on IBM hardware.

Legacy device tree used the reg property for the physical id of an spe.
This patch fixes find_spu_unit_number to look for the spu id in that order.
The length is checked to avoid misinterpretation in case the attributes
unit-id or reg do not contain the id.

Signed-off-by: Christian Krafft <krafft@de.ibm.com>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Cc: Jeremy Kerr <jk@ozlabs.org>