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.c b/plat/rockchip/rk3399/drivers/secure/secure.c
index f2e9ab0..d3c8cb8 100644
--- a/plat/rockchip/rk3399/drivers/secure/secure.c
+++ b/plat/rockchip/rk3399/drivers/secure/secure.c
@@ -163,7 +163,7 @@
 	mmio_write_32(SGRF_BASE + SGRF_SLV_SECURE_CON0_4(3),
 		      SGRF_SLV_S_WMSK | SGRF_SLV_S_ALL_NS);
 	mmio_write_32(SGRF_BASE + SGRF_SLV_SECURE_CON0_4(4),
-		      SGRF_SLV_S_WMSK | SGRF_SLV_S_ALL_NS);
+		      SGRF_SLV_S_WMSK | SGRF_INTSRAM_S);
 }
 
 void secure_sgrf_ddr_rgn_init(void)