MAINTAINERS: merge SWIOTLB SUBSYSTEM into DMA MAPPING HELPERS

Commit 78013eaadf ("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 <lukas.bulwahn@gmail.com>
Acked-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

MAINTAINERS

@@ -6147,6 +6147,7 @@ F:	include/asm-generic/dma-mapping.h
 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
@@ -19581,16 +19582,6 @@ S:	Maintained
 F:	Documentation/admin-guide/svga.rst
 F:	arch/x86/boot/video*
 
-SWIOTLB SUBSYSTEM
-M:	Christoph Hellwig <hch@infradead.org>
-L:	iommu@lists.linux.dev
-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 <jiri@resnulli.us>
 M:	Ivan Vecera <ivecera@redhat.com>
@@ -22286,8 +22277,10 @@ M:	Stefano Stabellini <sstabellini@kernel.org>
 L:	xen-devel@lists.xenproject.org (moderated for non-subscribers)
 L:	iommu@lists.linux.dev
 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
 
 XFS FILESYSTEM
 C:	irc://irc.oftc.net/xfs