main: introduce --output-format option for rauc info
main: introduce --output-format option for rauc info

Preparation for allowing different output format types, currently
supported only 'readable'.

Signed-off-by: Enrico Jorns <a2e5f936c390f36494e46e71bcfbe365bb1e8c49@pengutronix.de>

ejoerns/rauc,jluebbe/rauc,rauc/rauc,ejoerns/rauc,jluebbe/rauc,jluebbe/rauc,ejoerns/rauc,rauc/rauc,rauc/rauc