dm: Kconfig: Move CONFIG_SYS_MALLOC_F_LEN to Kconfig

Move this option to Kconfig and update all boards.
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/Linksprite_pcDuino3_fdt_defconfig b/configs/Linksprite_pcDuino3_fdt_defconfig
index cfed375..1e749cd 100644
--- a/configs/Linksprite_pcDuino3_fdt_defconfig
+++ b/configs/Linksprite_pcDuino3_fdt_defconfig
@@ -13,3 +13,5 @@
 +S:CONFIG_DRAM_CLK=480
 +S:CONFIG_DRAM_ZQ=122
 +S:CONFIG_DRAM_EMR1=4
+CONFIG_SYS_MALLOC_F=y
+CONFIG_SYS_MALLOC_F_LEN=0x400