arm/xen: Introduce xen_setup_dma_ops()

This patch introduces new helper and places it in new header.
The helper's purpose is to assign any Xen specific DMA ops in
a single place. For now, we deal with xen-swiotlb DMA ops only.
The one of the subsequent commits in current series will add
xen-grant DMA ops case.

Also re-use the xen_swiotlb_detect() check on Arm32.

Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
[For arm64]
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/1654197833-25362-2-git-send-email-olekstysh@gmail.com
Signed-off-by: Juergen Gross <jgross@suse.com>

arch/arm/mm/dma-mapping.c

@@ -33,7 +33,7 @@
 #include <asm/dma-iommu.h>
 #include <asm/mach/map.h>
 #include <asm/system_info.h>
-#include <xen/swiotlb-xen.h>
+#include <asm/xen/xen-ops.h>
 
 #include "dma.h"
 #include "mm.h"
@@ -2287,10 +2287,7 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
 
 	set_dma_ops(dev, dma_ops);
 
-#ifdef CONFIG_XEN
-	if (xen_initial_domain())
-		dev->dma_ops = &xen_swiotlb_dma_ops;
-#endif
+	xen_setup_dma_ops(dev);
 	dev->archdata.dma_ops_setup = true;
 }