MAINTAINERS: add related dts to IXP4xx

get_maintainer.pl currently give no maintainer on all IXP4xx DTS files.
Add them to the set of files handled by IXP4xx maintainers.
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20221005105734.3513581-1-clabbe@baylibre.com
Link: https://lore.kernel.org/r/20221214204223.177807-1-linus.walleij@linaro.orgSigned-off-by: Arnd Bergmann <arnd@arndb.de>

MAINTAINERS

@@ -2266,6 +2266,7 @@ F:	Documentation/devicetree/bindings/bus/intel,ixp4xx-expansion-bus-controller.y
 F:	Documentation/devicetree/bindings/gpio/intel,ixp4xx-gpio.txt
 F:	Documentation/devicetree/bindings/interrupt-controller/intel,ixp4xx-interrupt.yaml
 F:	Documentation/devicetree/bindings/timer/intel,ixp4xx-timer.yaml
+F:	arch/arm/boot/dts/intel-ixp*
 F:	arch/arm/mach-ixp4xx/
 F:	drivers/bus/intel-ixp4xx-eb.c
 F:	drivers/clocksource/timer-ixp4xx.c