kvm: powerpc: e500: mark page accessed when mapping a guest page

Mark the guest page as accessed so that there is likely
less chances of this page getting swap-out.

Signed-off-by: Bharat Bhushan <bharat.bhushan@freescale.com>
Acked-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>