ARM: i.MX: provide declaration for board_spi_cs_gpio

Provide a public declaration of the board_spi_cs_gpio()
callback for i.MX SPI chip selects to prevent the warning
"Should it be static?" when compiling with "make C=1".

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>
diff --git a/board/genesi/mx51_efikamx/efikamx.c b/board/genesi/mx51_efikamx/efikamx.c
index 137e4ed..6ba55cd 100644
--- a/board/genesi/mx51_efikamx/efikamx.c
+++ b/board/genesi/mx51_efikamx/efikamx.c
@@ -14,6 +14,7 @@
 #include <asm/arch/sys_proto.h>
 #include <asm/arch/crm_regs.h>
 #include <asm/arch/clock.h>
+#include <asm/imx-common/spi.h>
 #include <i2c.h>
 #include <mmc.h>
 #include <fsl_esdhc.h>