powerpc/board/t1024rdb: enable board-level reset when issuing reset command

As board-specific reset logic, it needs to issue reset signal
via CPLD when issuing 'reset' command in u-boot, this patch
solves the issue of reset command not working on T1024RDB.

Signed-off-by: Shengzhou Liu <Shengzhou.Liu@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>