iommu/amd: Fix race in increase_address_space()/fetch_pte()

iommu/amd: Fix race in increase_address_space()/fetch_pte()

The 'pt_root' and 'mode' struct members of 'struct protection_domain'
need to be get/set atomically, otherwise the page-table of the domain
can get corrupted.

Merge the fields into one atomic64_t struct member which can be
get/set atomically.

Fixes: 2631cc0e2db1 ("iommu/amd: Relax locking in dma_ops path")
Reported-by: Qian Cai <cai@lca.pw>
Signed-off-by: Joerg Roedel <jroedel@suse.de>
Tested-by: Qian Cai <cai@lca.pw>
Link: https://lore.kernel.org/r/20200504125413.16798-2-joro@8bytes.org
Signed-off-by: Joerg Roedel <jroedel@suse.de>