arm: Add warnings about using gdata

We need to get rid of this SPL-specific setting of the global_data pointer.
It is already set up in start.S immediately before board_init_f() is called,
and there may be information there that is needed (e.g. pre-reloc malloc
info).

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

arch/arm/lib/spl.c

@@ -15,6 +15,11 @@
 
 /* Pointer to as well as the global data structure for SPL */
 DECLARE_GLOBAL_DATA_PTR;
+
+/*
+ * WARNING: This is going away very soon. Don't use it and don't submit
+ * pafches that rely on it. The global_data area is set up in crt0.S.
+ */
 gd_t gdata __attribute__ ((section(".data")));
 
 /*
@@ -28,7 +33,7 @@ void __weak board_init_f(ulong dummy)
 	/* Clear the BSS. */
 	memset(__bss_start, 0, __bss_end - __bss_start);
 
-	/* Set global data pointer. */
+	/* TODO: Remove settings of the global data pointer here */
 	gd = &gdata;
 
 	board_init_r(NULL, 0);