make fitImage configuration signature algorithm selectable with
FIT_SIGN_ALG.
(From OE-Core rev: e24b27a2b49e97cec6153f2d642d17a901b8ba12)
Signed-off-by: Richard Leitner <richard.leitner@skidata.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>