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/freescale/mx51evk/mx51evk.c b/board/freescale/mx51evk/mx51evk.c
index a88ff8f..9e8a02e 100644
--- a/board/freescale/mx51evk/mx51evk.c
+++ b/board/freescale/mx51evk/mx51evk.c
@@ -15,6 +15,7 @@
 #include <asm/arch/clock.h>
 #include <asm/mach-imx/mx5_video.h>
 #include <i2c.h>
+#include <input.h>
 #include <mmc.h>
 #include <fsl_esdhc.h>
 #include <power/pmic.h>