linux-phytec-fsl

xen: add page_to_mfn()

pfn_to_mfn(page_to_pfn(p)) is a common use case so add a generic
helper for it.

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>