Since af06d66ee32b (x86: fix setup of PVH Dom0 memory map) in Xen, PVH
dom0 need only use the memory memory provided by Xen which has already
setup all the correct holes.

xen_memory_setup() then ends up being trivial for a PVH guest so
introduce a new function (xen_auto_xlated_memory_setup()).
Signed-off-by: NDavid Vrabel <david.vrabel@citrix.com>
Acked-by: NRoger Pau Monné <roger.pau@citrix.com>
Tested-by: NRoger Pau Monné <roger.pau@citrix.com>