rockchip: update ROCKCHIP_SPL_RESERVE_IRAM to 0

Only rk3399 atf need ROCKCHIP_SPL_RESERVE_IRAM. This commit updates
its default setting to 0 so that other SoCs do not need to define it.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
diff --git a/configs/firefly-rk3399_defconfig b/configs/firefly-rk3399_defconfig
index 731222c..b8d0654 100644
--- a/configs/firefly-rk3399_defconfig
+++ b/configs/firefly-rk3399_defconfig
@@ -4,6 +4,7 @@
 CONFIG_SPL_LIBGENERIC_SUPPORT=y
 CONFIG_SYS_MALLOC_F_LEN=0x4000
 CONFIG_ROCKCHIP_RK3399=y
+CONFIG_ROCKCHIP_SPL_RESERVE_IRAM=0x4000
 CONFIG_SPL_STACK_R_ADDR=0x80000
 CONFIG_DEFAULT_DEVICE_TREE="rk3399-firefly"
 CONFIG_DEBUG_UART=y