arm: socfpga: Fixes: include <debug_uart.h>

Fix compilation warning when enable CONFIG_DEBUG_UART.

arch/arm/mach-socfpga/spl_s10.c: In function ‘board_init_f’:
arch/arm/mach-socfpga/spl_s10.c:146:2: warning: implicit declaration of function ‘debug_uart_init’; did you mean ‘part_init’? [-Wimplicit-function-declaration]
  debug_uart_init();

Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>

arch/arm/mach-socfpga/spl_s10.c

@@ -8,6 +8,7 @@
 #include <asm/u-boot.h>
 #include <asm/utils.h>
 #include <common.h>
+#include <debug_uart.h>
 #include <image.h>
 #include <spl.h>
 #include <asm/arch/clock_manager.h>