dom0/pvh: align allocation and mapping order to start address

dom0/pvh: align allocation and mapping order to start address

The p2m and iommu mapping code always had the requirement that
addresses and orders must be aligned when populating the p2m or the
iommu page tables.

PVH dom0 builder didn't take this requirement into account, and can
call into the p2m/iommu mapping helpers with addresses and orders that
are not aligned.

Fix this by making sure the orders passed to the physmap population
helpers are always aligned to the guest address to be populated.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Juergen Gross <jgross@suse.com>