imx: Include <input.h> header file

When building with W=1 errors like the one below is seen:

board/freescale/mx6sabresd/mx6sabresd.c:546:5: warning:
no previous prototype for ‘overwrite_console’
[-Wmissing-prototypes] int overwrite_console(void)

Fix the build warnings by including <input.h>.

Signed-off-by: Diego Dorta <diego.dorta@nxp.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
diff --git a/board/embest/mx6boards/mx6boards.c b/board/embest/mx6boards/mx6boards.c
index 8674599..ae04f68 100644
--- a/board/embest/mx6boards/mx6boards.c
+++ b/board/embest/mx6boards/mx6boards.c
@@ -26,6 +26,7 @@
 #include <asm/mach-imx/spi.h>
 #include <asm/mach-imx/video.h>
 #include <i2c.h>
+#include <input.h>
 #include <mmc.h>
 #include <fsl_esdhc.h>
 #include <miiphy.h>