KVM: PPC: booke: Extend MAS2 EPN mask for 64-bit

Extend MAS2 EPN mask to retain most significant bits on 64-bit hosts.
Use this mask in tlb effective address accessor.

Signed-off-by: Mihai Caraman <mihai.caraman@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>