malloc: Avoid defining calloc()

The C runtime calls malloc() before starting main(), e.g. to get some
memory to use for dynamic linking.

If CONFIG_TPL_SYS_MALLOC_SIMPLE is enabled, the calloc() symbol is
defined within U-Boot. The C runtime may call that too.

Use the same #define technique as for malloc_simple(), to fix a crash
on my machine when running:

   /tmp/b/sandbox_vpl/tpl/u-boot-tpl -D

This does not happen in CI, perhaps because the C runtime uses malloc()
instead of calloc().

Signed-off-by: Simon Glass <sjg@chromium.org>

common/malloc_simple.c

@@ -65,7 +65,7 @@ void *memalign_simple(size_t align, size_t bytes)
 }
 
 #if CONFIG_IS_ENABLED(SYS_MALLOC_SIMPLE)
-void *calloc(size_t nmemb, size_t elem_size)
+void *calloc_simple(size_t nmemb, size_t elem_size)
 {
 	size_t size = nmemb * elem_size;
 	void *ptr;

include/malloc.h

@@ -882,6 +882,7 @@ void malloc_disable_testing(void);
 #if CONFIG_IS_ENABLED(SYS_MALLOC_SIMPLE)
 #define malloc malloc_simple
 #define realloc realloc_simple
+#define calloc calloc_simple
 #define memalign memalign_simple
 #if IS_ENABLED(CONFIG_VALGRIND)
 #define free free_simple