image: Drop IMAGE_ENABLE_FIT

Make use of the host Kconfig for FIT. With this we can use
CONFIG_IS_ENABLED(FIT) directly in the host build, so drop the unnecessary
indirection.

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