MAINTAINERS: merge SWIOTLB SUBSYSTEM into DMA MAPPING HELPERS

Commit 78013eaadf69 ("x86: remove the IOMMU table infrastructure")
refactored the generic swiotlb/swiotlb-xen setup into pci-dma.c, but
misses to adjust MAINTAINERS.

Hence, ./scripts/get_maintainer.pl --self-test=patterns complains about
broken references.

As only include/linux/swiotlb.h is unique to the SWIOTLB SUBSYSTEM section
and Christoph is maintainer of DMA MAPPING HELPERS and SWIOTLB SUBSYSTEM,
just merge those two sections.

Leave the small architecture-dependent pieces to the arch maintainers.

Further, update the XEN SWIOTLB SUBSYSTEM to include all swiotlb-xen
headers and replace the pattern in drivers with the specific one file that
matches this pattern.

Signed-off-by: Lukas Bulwahn <[e-mail]>
Acked-by: Juergen Gross <[e-mail]>
Signed-off-by: Christoph Hellwig <[e-mail]>

MAINTAINERS

···
 F:	include/linux/dma-direct.h
 F:	include/linux/dma-mapping.h
 F:	include/linux/dma-map-ops.h
+F:	include/linux/swiotlb.h
 F:	kernel/dma/
 
 DMA MAPPING BENCHMARK
···
 F:	Documentation/admin-guide/svga.rst
 F:	arch/x86/boot/video*
 
-SWIOTLB SUBSYSTEM
-M:	Christoph Hellwig <[e-mail]>
-L:	[e-mail]
-S:	Supported
-W:	http://git.infradead.org/users/hch/dma-mapping.git
-T:	git git://git.infradead.org/users/hch/dma-mapping.git
-F:	arch/*/kernel/pci-swiotlb.c
-F:	include/linux/swiotlb.h
-F:	kernel/dma/swiotlb.c
-
 SWITCHDEV
 M:	Jiri Pirko <[e-mail]>
 M:	Ivan Vecera <[e-mail]>
···
 L:	[e-mail] (moderated for non-subscribers)
 L:	[e-mail]
 S:	Supported
-F:	arch/x86/xen/*swiotlb*
-F:	drivers/xen/*swiotlb*
+F:	arch/*/include/asm/xen/swiotlb-xen.h
+F:	drivers/xen/swiotlb-xen.c
+F:	include/xen/arm/swiotlb-xen.h
+F:	include/xen/swiotlb-xen.h
 
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