Add trace support to generic board

Add hooks for tracing to generic board, including:

- allow early tracing to start early as possible in U-Boot
- reserve memory for trace buffer
- copy early trace buffer to main trace buffer after relocation
- setup full tracing support after relocation

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

include/asm-generic/global_data.h

@@ -82,6 +82,9 @@ typedef struct global_data {
 	unsigned long fdt_size;	/* Space reserved for relocated FDT */
 	void **jt;		/* jump table */
 	char env_buf[32];	/* buffer for getenv() before reloc. */
+#ifdef CONFIG_TRACE
+	void		*trace_buff;	/* The trace buffer */
+#endif
 	struct arch_global_data arch;	/* architecture-specific data */
 } gd_t;
 #endif