spl: Use SYS_MALLOC_F instead of SYS_MALLOC_F_LEN

Use the new SPL/TPL/VPL_SYS_MALLOC_F symbols to determine whether the
malloc pool exists.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Sean Anderson <sean.anderson@seco.com>
diff --git a/common/Makefile b/common/Makefile
index 5c16172..cdeadf7 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -74,11 +74,7 @@
 
 obj-$(CONFIG_CROS_EC) += cros_ec.o
 obj-y += dlmalloc.o
-ifdef CONFIG_SYS_MALLOC_F
-ifneq ($(CONFIG_$(SPL_TPL_)SYS_MALLOC_F_LEN),0x0)
-obj-y += malloc_simple.o
-endif
-endif
+obj-$(CONFIG_$(SPL_TPL_)SYS_MALLOC_F) += malloc_simple.o
 
 obj-$(CONFIG_CYCLIC) += cyclic.o
 obj-$(CONFIG_$(SPL_TPL_)EVENT) += event.o