Add a cputable entry for the POWER7 processor.

Also tell firmware that we know about POWER7.
Signed-off-by: NMichael Neuling <mikey@neuling.org>
Signed-off-by: NJoel Schopp <jschopp@austin.ibm.com>
Signed-off-by: NPaul Mackerras <paulus@samba.org>