powerpc: Update page-in counter for CMM

A new field has been added to the VPA as a method for the client OS to
communicate to firmware the number of page-ins it is performing when
running collaborative memory overcommit.  The hypervisor will use this
information to better determine if a partition is experiencing memory
pressure and needs more memory allocated to it.

Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>