iommu/omap: Switch pagetable debugfs entry to use seq_file

The debugfs entry 'pagetable' that shows the page table entry
(PTE) data currently outputs only data that can be fit into a
page. Switch the entry to use the seq_file interface so that
it can show all the valid page table entries.

The patch also corrected the output for L2 entries, and prints
the proper L2 PTE instead of the previous L1 page descriptor
pointer.

Signed-off-by: Suman Anna <s-anna@ti.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>