s390x/pci: fixup the code walking IOMMU tables

s390x/pci: fixup the code walking IOMMU tables

Current s390x PCI IOMMU code is lack of flags' checking, including:
1) protection bit
2) table length
3) table offset
4) intermediate tables' invalid bit
5) format control bit

This patch introduces a new struct named S390IOTLBEntry, and makes up
these missed checkings. At the same time, inform the guest with the
corresponding error number when the check fails. Finally, in order to
get the error number, we export s390_guest_io_table_walk().

Reviewed-by: Pierre Morel <[email protected]>
Signed-off-by: Yi Min Zhao <[email protected]>
Message-Id: <20180205072258[email protected]>
Signed-off-by: Cornelia Huck <[email protected]>