Add print_freq() to display frequencies nicely

Add a function similar to print_size() that works for frequencies. It can
handle from Hz to GHz.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>

include/display_options.h

@@ -22,6 +22,17 @@
  */
 void print_size(uint64_t size, const char *suffix);
 
+/**
+ * print_freq() - Print a frequency with a suffix
+ *
+ * Print frequencies as "x.xx GHz", "xxx KHz", etc as needed; allow for
+ * optional trailing string (like "\n")
+ *
+ * @freq:	Frequency to print in Hz
+ * @suffix	String to print after the frequency
+ */
+void print_freq(uint64_t freq, const char *suffix);
+
 /**
  * print_buffer() - Print data buffer in hex and ascii form
  *