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/pcm051_rev3_defconfig b/configs/pcm051_rev3_defconfig
index 27ad6ff..b5c62a6 100644
--- a/configs/pcm051_rev3_defconfig
+++ b/configs/pcm051_rev3_defconfig
@@ -2,3 +2,5 @@
 CONFIG_SYS_EXTRA_OPTIONS="REV3"
 +S:CONFIG_ARM=y
 +S:CONFIG_TARGET_PCM051=y
+CONFIG_SYS_MALLOC_F=y
+CONFIG_SYS_MALLOC_F_LEN=0x400