binman: implement signing FIT images during image build

The patch implement new property 'fit,sign' that can be declared
at the top-level 'fit' node. If that option is declared, fit tryies
to detect private keys directory among binman include directories.
That directory than passed to mkimage using '-k' flag and that enable
signing of FIT.

Signed-off-by: Alexander Kochetkov <al.kochet@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Renumbered files, moved new tests to end:
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/binman/test/340_rsa2048.key b/tools/binman/test/340_rsa2048.key
new file mode 100644
index 0000000..e74b20c
--- /dev/null
+++ b/tools/binman/test/340_rsa2048.key
@@ -0,0 +1,28 @@
+-----BEGIN PRIVATE KEY-----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+XdphOEENrPwoe9ATWIyBpT/wDrEz3L6JbE9dWMYY8vKYESt3qhVqDlbpmnYl8Jm+
+O3r5Cy2NlJMCgYEAyqzsCZuy5QcesnByvm8dqpxdxdkzJYu9wyakfKZj+gUgfO57
+OFOkjFk07yFB27MuPctCFredmfpDr+ygHRoPkG7AHw2Fss2EEaeP5bU18ilPQMqN
+vxVMs5EblVVUgJUVoVcsC2yz2f4S7oPOAk5BPoehOIzydauznWrvIAas7I8CgYBr
+CFHxLoNq6cbZQ3JACERZrIf2/vmZjoOHtoR1gKYRK7R1NmKDB7lihRMtCSBix/4/
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+eIUDbkW6NPQzmFOhtaw3k/gzq5Yd2v0M82iWAqiJRwKBgQCl2+e2cjISK31QhKTC
+puhwQ0/YuC3zlwMXQgB3nPw8b9RlaDTMrRBCIUFIrrX11tHswGWpyVsxW2AvZ3Zm
+jsWpwGkUdpRdXJBhSaisV/PA+x3kYhpibzEI8FrzhU69zNROCb8CTkN4WcdBdq6J
+PUh/jRtKoE79qrlnIlNvFoz2gQ==
+-----END PRIVATE KEY-----