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/cm_t335_defconfig b/configs/cm_t335_defconfig
index 5ff4f9c..5c1d3cf 100644
--- a/configs/cm_t335_defconfig
+++ b/configs/cm_t335_defconfig
@@ -1,3 +1,5 @@
 CONFIG_SPL=y
 +S:CONFIG_ARM=y
 +S:CONFIG_TARGET_CM_T335=y
+CONFIG_SYS_MALLOC_F=y
+CONFIG_SYS_MALLOC_F_LEN=0x400