iommupt: Documentation fixes

iommupt: Documentation fixes

Some adjustments pointed out by Randy:

 "decodes an full 64-bit" -> "decodes the full 64 bit"

 Correct the function parameter name for iova_to_phys()

 Use the recommended section heading style.

Suggested-by: Randy Dunlap <rdunlap@infradead.org>
Fixes: ab0b572847ac ("genpt: Add Documentation/ files")
Fixes: 879ced2bab1b ("iommupt: Add the AMD IOMMU v1 page table format")
Fixes: 9d4c274cd7d5 ("iommupt: Add iova_to_phys op")
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>