common/board_f.c: fix compile error when tracing disabled

When CONFIG_TRACE is disabled, linking fails with:

common/built-in.o:(.data.init_sequence_f+0x8): undefined reference to `trace_early_init'

To fix, wrap the call to trace_early_init() with #ifdef CONFIG_TRACE.

Cc: Simon Glass <sjg@chromium.org>
Cc: Tom Rini <trini@ti.com>
Signed-off-by: Kevin Hilman <khilman@linaro.org>

common/board_f.c

@@ -813,7 +813,9 @@ static init_fnc_t init_sequence_f[] = {
 #endif
 	setup_mon_len,
 	setup_fdt,
+#ifdef CONFIG_TRACE
 	trace_early_init,
+#endif
 	initf_malloc,
 #if defined(CONFIG_MPC85xx) || defined(CONFIG_MPC86xx)
 	/* TODO: can this go into arch_cpu_init()? */