image: Use Kconfig to enable CONFIG_FIT_VERBOSE on host

Add a host Kconfig for FIT_VERBOSE. With this we can use
CONFIG_IS_ENABLED(FIT_VERBOSE) directly in the tools build, so drop the
forcing of this in the image.h header.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>