iommu/io-pgtable-arm-v7s: Abort allocation when table address overflows the PTE

When run on a 64-bit system in selftest, the v7s driver may obtain page
table with physical addresses larger than 32-bit. Level-2 tables are 1KB
and are are allocated with slab, which doesn't accept the GFP_DMA32
flag. Currently map() truncates the address written in the PTE, causing
iova_to_phys() or unmap() to access invalid memory. Kasan reports it as
a use-after-free. To avoid any nasty surprise, test if the physical
address fits in a PTE before returning a new table. 32-bit systems,
which are the main users of this page table format, shouldn't see any
difference.

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>