iommu/amd: Rename struct amd_io_pgtable iopt to pgtbl

iommu/amd: Rename struct amd_io_pgtable iopt to pgtbl

There is struct protection_domain iopt and struct amd_io_pgtable iopt.
Next patches are going to want to write domain.iopt.iopt.xx which is quite
unnatural to read.

Give one of them a different name, amd_io_pgtable has fewer references so
call it pgtbl, to match pgtbl_cfg, instead.

Suggested-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/6-v2-831cdc4d00f3+1a315-amd_iopgtbl_jgg@nvidia.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>