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/Marvell/db-88f6820-amc/MAINTAINERS b/board/Marvell/db-88f6820-amc/MAINTAINERS
index abf5b7e..d519eb4 100644
--- a/board/Marvell/db-88f6820-amc/MAINTAINERS
+++ b/board/Marvell/db-88f6820-amc/MAINTAINERS
@@ -4,3 +4,4 @@
 F:	board/Marvell/db-88f6820-amc/
 F:	include/configs/db-88f6820-amc.h
 F:	configs/db-88f6820-amc_defconfig
+F:	configs/db-88f6820-amc_nand_defconfig