MAINTAINERS: Add some missing defconfig files to existing entries

We have a few places where defconfigs were added (or renamed) and not
included in their previously listed MAINTAINERS entry, correct this.

Signed-off-by: Tom Rini <trini@konsulko.com>
Acked-by:  Adam Ford <aford173@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/board/beacon/imx8mm/MAINTAINERS b/board/beacon/imx8mm/MAINTAINERS
index d48ba86..d8a5d09 100644
--- a/board/beacon/imx8mm/MAINTAINERS
+++ b/board/beacon/imx8mm/MAINTAINERS
@@ -5,4 +5,5 @@
 F:	board/beacon/imx8mm/
 F:	include/configs/imx8mm_beacon.h
 F:	configs/imx8mm_beacon_defconfig
+F:	configs/imx8mm_beacon_fspi_defconfig
 F:	doc/board/beacon/