image: Add Kconfig options for FIT in the tools build

In preparation for enabling CONFIG_IS_ENABLED() on the host build, add
some options to enable the various FIT options expected in these tools.
This will ensure that the code builds correctly when CONFIG_TOOLS_xxx
is distinct from CONFIG_xxx.

Drop some #ifdefs which are immediately unnecessary (many more are in
later patches).

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