main: introduce slotstate_to_str()
main: introduce slotstate_to_str()

Allows to get string representation of slot state, e.g. for status
printout.

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

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