mx31_3ds: Remove unused debug board definitions

In commit (c5d38f08): "mx31_3ds: revert 3ds debug board relate code"
the debug board definitions are placed in a separate file.

Remove the remaining debug board related define from mach-mx31_3ds.c.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Rogerio Pimentel <rogerio.pimentel@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>