uboot-imx

board: MCR3000: use new DM watchdog

This patch switches MCR3000 board to the new DM watchdog.

The change in u-boot.lds is because MCR3000.o grows a bit
with this patch and doesn't fit anymore below env_offset on
some versions of GCC.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>