Using a plain vanilla fighter from the PHB, you pick Str 14 for one of your stats, pick a race like Mountain Dwarf or Half-Orc that gives you +2 to Strength for a starting StengthStrength of 16. Use Half-Orc for Savage Attack (thanks to Someone_Evil for pointing that out).
CritialsCriticals: You get an extra d6 on these from Savage Attacker. You roll a total of 15 d20 (12 attacks with advantage, 3 Lucky dice), and have 1/20th on each to crit, so you add 15/20 * 4d6 from critical damage, or about 15.3 points (with Great Weapon Fighting style).
Possible Improvements. It may be possible to eke out a few more points of optimization here and there, maybe by taking Archery for the +2 to hit vs Great Weapon Fighting for the +1.33 damage from die rolls, but then you would need another way go get adavantageadvantage on your attacks, as Mounted Combatant only works for melee.
Goodguy5 reports that in the new Mordenkainen Presents, the once-a-turn limit has been lifted on the Bugbear's Surprise Attack. This makes a large difference: pick Bugbear instead of Half-Orc and add +2d6 to all six attacks for an extra 42 * 95.9% = 40.28. Replace 3.125 points on crits from 1d6 Savage Attacker, with 5.25 points from 2d6 SurpiseSurprise Attack, for another 2.125 and a total of +42.4 damage over the Half-Orc. This on top of the 192 gets you to 234 expected damage.