iommu-fixes-v5.8-rc5

Including:

	- Fix for a use-after-free of the device iommu-group. Found in the
	  arm-smmu driver, but the fix is in generic code.

	- Fix for the new Allwinner IOMMU driver to use the atomic
	  readl_timeout() variant in IO/TLB flushing code.

	- A couple of cleanups to fix various compile warnings.