parisc/agp: Use 64-bit LE values in SBA IOMMU PDIR table

The PDIR table of the System Bus Adapter (SBA) I/O MMU uses 64-bit
little-endian pointers.

Signed-off-by: Helge Deller <deller@gmx.de>
Cc: stable@vger.kernel.org # v6.4+