Make additional kernel parameters configurable

[kkaempf]

When building ISOs for aarch64 an additional console=ttyS0 gets added to the kernel arguments.

This works nicely for Raspberry Pi but breaks on other ARM systems, like Nvidia Jetson which requires ttyIC0

Instead of hard coding the serial console, it should (at least) be a runtime parameter of the build-iso command.

I couldn't easily find other ways of adding kernel parameters in the documentation :-(

[frelon]

Is this a duplicate of #1764 ?

[kkaempf]

Indeed !