rockchip: rk322x: use defconfig for SYS_MALLOC_F_LEN

There is no difference in rk322x board use for SYS_MALLOC_F_LEN,
so we can use default value.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
diff --git a/arch/arm/mach-rockchip/rk322x/Kconfig b/arch/arm/mach-rockchip/rk322x/Kconfig
index 60e99a7..9d734c3 100644
--- a/arch/arm/mach-rockchip/rk322x/Kconfig
+++ b/arch/arm/mach-rockchip/rk322x/Kconfig
@@ -12,7 +12,7 @@
 	default "rk322x"
 
 config SYS_MALLOC_F_LEN
-	default 0x400
+	default 0x800
 
 config SPL_SERIAL_SUPPORT
 	default y