Rename this function and the ones further down its
call-chain to domain_context_clear_*. In particular this
means:

	iommu_detach_dependent_devices -> domain_context_clear
		   iommu_detach_dev_cb -> domain_context_clear_one_cb
		      iommu_detach_dev -> domain_context_clear_one

These names match a lot better with its
domain_context_mapping counterparts.
Signed-off-by: NJoerg Roedel <jroedel@suse.de>