rockchip: rk3399: enable secure accessing for SRAM

Sorry to miss the security configuration for SRAM, if we don't support
it, somebody may modify the comment of SRAM in the non-secure space.
Let's fix this issue.

Signed-off-by: Xing Zheng <zhengxing@rock-chips.com>
diff --git a/plat/rockchip/rk3399/drivers/secure/secure.h b/plat/rockchip/rk3399/drivers/secure/secure.h
index 6eb2237..12a875c 100644
--- a/plat/rockchip/rk3399/drivers/secure/secure.h
+++ b/plat/rockchip/rk3399/drivers/secure/secure.h
@@ -62,6 +62,8 @@
 
 #define SGRF_PMUSRAM_S			BIT(8)
 
+#define SGRF_INTSRAM_S			BIT(13)
+
 /* ddr region */
 #define SGRF_DDR_RGN_0_16_WMSK		0x0fff  /* DDR RGN 0~16 size mask */