ARM: imx31: Remove remaining i.MX31 board code

i.MX31 is a devicetree only platform.

Remove remaining i.MX31 board code.

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

Author: fabioestevam