MAINTAINERS: Update Xen maintainership

Due to time constraints I am stepping down as maintainter. I will stay
as reviewer for x86 code (for which create a separate category).

Stefano is now maintainer for Xen hypervisor interface and Oleksandr has
graciously agreed to become a reviewer.
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
Acked-by: Juergen Gross <jgross@suse.com>
Acked-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Link: https://lore.kernel.org/r/1653674225-10447-1-git-send-email-boris.ostrovsky@oracle.comSigned-off-by: Juergen Gross <jgross@suse.com>

MAINTAINERS

@@ -21549,23 +21549,29 @@ F:	arch/arm64/include/asm/xen/
 F:	arch/arm64/xen/
 
 XEN HYPERVISOR INTERFACE
-M:	Boris Ostrovsky <boris.ostrovsky@oracle.com>
 M:	Juergen Gross <jgross@suse.com>
-R:	Stefano Stabellini <sstabellini@kernel.org>
+M:	Stefano Stabellini <sstabellini@kernel.org>
+R:	Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
 L:	xen-devel@lists.xenproject.org (moderated for non-subscribers)
 S:	Supported
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/xen/tip.git
 F:	Documentation/ABI/stable/sysfs-hypervisor-xen
 F:	Documentation/ABI/testing/sysfs-hypervisor-xen
-F:	arch/x86/include/asm/pvclock-abi.h
-F:	arch/x86/include/asm/xen/
-F:	arch/x86/platform/pvh/
-F:	arch/x86/xen/
 F:	drivers/*/xen-*front.c
 F:	drivers/xen/
 F:	include/uapi/xen/
 F:	include/xen/
 
+XEN HYPERVISOR X86
+M:	Juergen Gross <jgross@suse.com>
+R:	Boris Ostrovsky <boris.ostrovsky@oracle.com>
+L:	xen-devel@lists.xenproject.org (moderated for non-subscribers)
+S:	Supported
+F:	arch/x86/include/asm/pvclock-abi.h
+F:	arch/x86/include/asm/xen/
+F:	arch/x86/platform/pvh/
+F:	arch/x86/xen/
+
 XEN NETWORK BACKEND DRIVER
 M:	Wei Liu <wei.liu@kernel.org>
 M:	Paul Durrant <paul@xen.org>