malloc_simple: Add Kconfig option for using only malloc_simple in the SPL

common/dlmalloc.c is quite big, both in .text and .data usage, therefor
on some boards the SPL is build to use only malloc_simple.c and not the
dlmalloc.c code. This is done in various include/configs/foo.h with the
following construct:

 #ifdef CONFIG_SPL_BUILD
 #define CONFIG_SYS_MALLOC_SIMPLE
 #endif

This commit introduces a SPL_MALLOC_SIMPLE Kconfig bool which allows
selecting this functionality through Kconfig instead.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Simon Glass <sjg@chromium.org>

Kconfig

@@ -114,6 +114,16 @@ config SPL
 	help
 	  If you want to build SPL as well as the normal image, say Y.
 
+config SPL_SYS_MALLOC_SIMPLE
+	bool
+	depends on SPL
+	prompt "Only use malloc_simple functions in the spl"
+	help
+	  Say Y here to only use the *_simple malloc functions from
+	  malloc_simple.c, rather then using the versions from dlmalloc.c
+	  this will make the SPL binary smaller at the cost of more heap
+	  usage as the *_simple malloc functions do not re-use free-ed mem.
+
 config SPL_STACK_R
 	depends on SPL
 	bool "Enable SDRAM location for SPL stack"