spl: Add a name to the SPL load-image methods

It is useful to name each method so that we can print out this name when
using the method. Currently this happens using a separate function. In
preparation for unifying this, add a name to each method.

The name is only available if we have libcommon support (i.e can use
printf()).

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