ARM: imx: imx31moboard: Include "board-mx31moboard.h" header file

The following build warnings are seen with W=1:

warning: no previous prototype for ‘mx31moboard_devboard_init’
[-Wmissing-prototypes] void __init mx31moboard_devboard_init(void)
warning: no previous prototype for ‘mx31moboard_marxbot_init’
[-Wmissing-prototypes] void __init mx31moboard_marxbot_init(void)

Fix these warnings by including "board-mx31moboard.h".

Signed-off-by: Marco Franchi <marco.franchi@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>