iommu/amd: Enable swiotlb in all cases

Previously the AMD IOMMU would only enable SWIOTLB in certain
circumstances:
 * IOMMU in passthrough mode
 * SME enabled

This logic however doesn't work when an untrusted device is plugged in
that doesn't do page aligned DMA transactions.  The expectation is
that a bounce buffer is used for those transactions.

This fails like this:

swiotlb buffer is full (sz: 4096 bytes), total 0 (slots), used 0 (slots)

That happens because the bounce buffers have been allocated, followed by
freed during startup but the bounce buffering code expects that all IOMMUs
have left it enabled.

Remove the criteria to set up bounce buffers on AMD systems to ensure
they're always available for supporting untrusted devices.

Fixes: 82612d66 ("iommu: Allow the dma-iommu api to use bounce buffers")
Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20220404204723.9767-2-mario.limonciello@amd.comSigned-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/amd/iommu.c

@@ -1838,17 +1838,10 @@ void amd_iommu_domain_update(struct protection_domain *domain)
 	amd_iommu_domain_flush_complete(domain);
 }
 
-static void __init amd_iommu_init_dma_ops(void)
-{
-	swiotlb = (iommu_default_passthrough() || sme_me_mask) ? 1 : 0;
-}
-
 int __init amd_iommu_init_api(void)
 {
 	int err;
 
-	amd_iommu_init_dma_ops();
-
 	err = bus_set_iommu(&pci_bus_type, &amd_iommu_ops);
 	if (err)
 		return err;