ARM: meson: enable FIT with LEGACY_IMAGE_FORMAT on all configs

Allow all boards to boot with a fitImage, but keep support for
Legacy image format for now.

Link: https://lore.kernel.org/r/20231023-usb-dfu-boot-v1-1-df9d121c67c1@linaro.org


Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>