The mbedtls library is used by the binding crate, so move the submodule
into this directory as well.
Signed-off-by: David Brown <david.brown@linaro.org>
Create a crate `mcuboot-sys` to hold the building and binding of the
mcuboot code. There aren't any substantive code changes here, just
moving the code into a separate crate.
Signed-off-by: David Brown <david.brown@linaro.org>