README: Remove CONFIG_SYS_MALLOC_F_LEN comment

This option is now widely available, so remove the comment that it is only
available on ARM and sandbox.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/README b/README
index 26d5ad2..e906253 100644
--- a/README
+++ b/README
@@ -3835,9 +3835,6 @@
 		The memory will be freed (or in fact just forgotten) when
 		U-Boot relocates itself.
 
-		Pre-relocation malloc() is only supported on ARM and sandbox
-		at present but is fairly easy to enable for other archs.
-
 - CONFIG_SYS_MALLOC_SIMPLE
 		Provides a simple and small malloc() and calloc() for those
 		boards which do not use the full malloc in SPL (which is