[POWERPC] Add 'model: ...' line to common show_cpuinfo()

Print out 'model' property of '/' node as a machine name
in generic show_cpuinfo() routine.

Signed-off-by: Marian Balakowicz <m8@semihalf.com>
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Paul Mackerras <paulus@samba.org>