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>