driver core: Replace dev->dma_iommu with dev_dma_iommu()

driver core: Replace dev->dma_iommu with dev_dma_iommu()

In C, bitfields are not necessarily safe to modify from multiple
threads without locking. Switch "dma_iommu" over to the "flags" field
so modifications are safe.

Cc: Leon Romanovsky <leon@kernel.org>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Christoph Hellwig <hch@lst.de>
Reviewed-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>
Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patch.msgid.link/20260406162231.v5.3.Id20d5973cbff542fea290e13177e9423f5d81342@changeid
Signed-off-by: Danilo Krummrich <dakr@kernel.org>