rockchip: move SYS_MALLOC_F_LEN to rk3288 own Kconfig

since different rockchip SOC have different size of SRAM,
So the size SYS_MALLOC_F_LEN may different, so move this
config to rk3288 own Kconfig

Signed-off-by: Lin Huang <hl@rock-chips.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/mach-rockchip/rk3288/Kconfig b/arch/arm/mach-rockchip/rk3288/Kconfig
index 4d0f1b5..d0a7276 100644
--- a/arch/arm/mach-rockchip/rk3288/Kconfig
+++ b/arch/arm/mach-rockchip/rk3288/Kconfig
@@ -19,6 +19,9 @@
 config SYS_SOC
 	default "rockchip"
 
+config SYS_MALLOC_F_LEN
+	default 0x0800
+
 source "board/google/chromebook_jerry/Kconfig"
 
 source "board/firefly/firefly-rk3288/Kconfig"