src/main: fix missing argument conditionals
src/main: fix missing argument conditionals

Display a warning about missing arguments only when they are really
missing, otherwise this will confuse.

Also error on excess arguments.

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

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