[POWERPC] powerpc: Workaround for of_platform without "reg" nor "dcr-reg"

Devices with no "reg" nor "dcr-reg" property are given a bus_id which
is the node name alone. This means that if more than one such device
with the same names are present in the system, sysfs will have
collisions when creating the symlinks and will fail registering the
devices.

This works around that problem by assigning successive numbers to such
devices.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>