rockchip: evk_rk3308: Cleanup headers

There is no user of 'gd', so drop the usage of DECLARE_GLOBAL_DATA_PTR
and the including of 'asm/global_data.h'. Also include correct headers
to avoid build error.

Signed-off-by: Peng Fan <peng.fan@nxp.com>

board/rockchip/evb_rk3308/evb_rk3308.c

@@ -4,9 +4,8 @@
  */
 
 #include <adc.h>
-#include <asm/global_data.h>
-
-DECLARE_GLOBAL_DATA_PTR;
+#include <stdio.h>
+#include <linux/kernel.h>
 
 #define KEY_DOWN_MIN_VAL        0
 #define KEY_DOWN_MAX_VAL        30