boot: Support booti format in bootm

boot: Support booti format in bootm

At present the booti format is handled separately, in its own command.
Provide a way to boot uncompressed booti images within the bootm code,
so that eventually we can boot these images without CONFIG_CMDLINE

Update bootm_init() to attach the images for all formats which use them.

Add some debugging while we are here.

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