The current usage pattern of image_probe() is a legacy from the time
before commit 34b6ecb ("[image] Simplify image management") when
loading an image to its executable location in memory was a separate
action from actually executing the image.

Call image_probe() as soon as an image is registered.  This allows
"imgstat" to display image type information for all images and allows
image-consuming code to assume that image->type is already set
correctly.

Ignore failures if image_probe() does not recognise the image, since
we do expect to handle unrecognised images (initrds, modules, etc).
Unrecognised images will be left with a NULL image->type, which
image-consuming code can easily check.

Signed-off-by: Michael Brown <mcb30@ipxe.org>