If someone was physically hanging off of a cliff at the end of the season, then yes, you could say that the ending was "literally" a cliff-hanger. You wouldn't say that the whole season was a cliff-hanger, though. You could say that the "last episode" was a cliff-hanger, or the "end of the season" was a cliff-hanger, or "the season ended with a cliff-hanger."

Literally is one of the most misused words these days. When you use it, you are saying that your words are not an expression or a figure of speech. If it's literally a cliff-hanger, then there is an actual person hanging from an actual cliff. Gray's comment is also true. A season can end with a cliffhanger, but the season as a whole isn't a cliffhanger. A cliffhanger ending, if this wasn't made clear, is where an episode finishes, leaving the story unresolved. The classic example was the batman series from the 1960s. At the end of every episode, batman would be trapped and facing certain death. We would then be told to tune in next time to see if he survives. The next episode would then finish the story from the previous episode and start a new story to leave unfinished for the next day. These days it is common for a season the have a cliffhanger ending but not every episode.