kvm: powerpc: define a linux pte lookup function

We need to search linux "pte" to get "pte" attributes for setting TLB in KVM.
This patch defines a lookup_linux_ptep() function which returns pte pointer.

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