bdinfo: Export some basic printing functions

At present the functions to print a number and a frequency are static. We
want to move some of the code in here to an arch-specific file. For
consistency that code should use these same functions. So export them with
an appropriate name.

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