[POWERPC] Remove linux,device properties

The linux,device property isn't used anywhere within the kernel, and
since it's a kernel pointer, it's a little useless for userspace.

This change removes the code to create this property in
of_device_register.

Built for pmac32.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>