board: freescale: t4rdb: Add MAINTAINER

Add "Priyanka Jain <priyanka.jain@nxp.com>" as
MAINTAINER for t4rdb board.

Signed-off-by: Priyanka Jain <priyanka.jain@nxp.com>

board/freescale/t4rdb/MAINTAINERS

 T4RDB BOARD
-#M:	Chunhe Lan <Chunhe.Lan@freescale.com>
-S:	Orphan (since 2018-05)
+M:	Priyanka Jain <priyanka.jain@nxp.com>
+S:	Maintained
 F:	board/freescale/t4rdb/
 F:	include/configs/T4240RDB.h
 F:	configs/T4160RDB_defconfig