efi: Correct dependency on FIT_SIGNATURE

efi: Correct dependency on FIT_SIGNATURE

At present EFI_SECURE BOOT selects RSA but does not necessarily enable
FIT_SIGNATURE. Mostly this is fine, but a few boards do not enable it,
so U-Boot tries to do RSA verification when loading FIT images, but it
is not enabled.

This worked because the condition for checking the RSA signature is
wrong in the fit_image_verify_with_data() function. In order to fix it
we need to fix this dependency. Make sure that FIT_SIGNATURE is enabled
so that RSA can be used.

It might be better to avoid using 'select' in this situation.

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