specifying intermediate certificates in bundle.bbclass

[hellow554]

According to the docs if you'd like to include intermediate certificates you have to use --intermediate=your/cert/here.pem, but the bundle.bbclass does not provide such option.

One could misuse the BUNDLE_ARGS variable to acomplish this.

I propose a RAUC_INTERMEDIATE_FILE (or RAUC_INTER_FILE for short, although I'd like to see the longer version) that will automatically add an intermediate file to the rauc bundle command.

[ejoerns]

I'd tend to agree with you, as we are currently in the process of introducing this in pengutronix/genimage#139 accordingly (which is the comparable mechanism used for PTXdist).

But we must also take care here that this option can be called multiple times to add multiple intermediate certs. Thus the variable must be a list and evaluated as such. Due to this, I am not fully sure if this is a benefit over simply giving the explicit options with BUNDLE_ARGS (but it could as it is consistent with providing key and cert via variables, too).