iommu-fixes-5.4-rc1

A couple of fixes for the AMD IOMMU driver have piled up:

	* Some fixes for the reworked IO page-table which caused memory
	  leaks or did not allow to downgrade mappings under some
	  conditions.

	* Locking fixes to fix a couple of possible races around
	  accessing 'struct protection_domain'. The races got introduced
	  when the dma-ops path became lock-less in the fast-path.