rockchip: rk3399: spl: Mark printascii into debug

Now, we have spl_board_init with preloader_console_init that
indeed show SPL banner.

So mark the 'U-Boot SPL board init' print into debug.
Signed-off-by: NJagan Teki <jagan@amarulasolutions.com>
Reviewed-by: NKever Yang <kever.yang@rock-chips.com>

arch/arm/mach-rockchip/rk3399-board-spl.c

@@ -164,7 +164,7 @@ void board_init_f(ulong dummy)
 	 * printhex8(0x1234);
 	 * printascii("string");
 	 */
-	printascii("U-Boot SPL board init\n");
+	debug("U-Boot SPL board init\n");
 #endif
 
 	ret = spl_early_init();