This one took me a while to figure out as well. It's not obvious at all. And apologies if anything is unclear, I kind of did it by accident so I'm going by memory.
Basically you have to follow the story chain:
1) Claim the Griffon Wing keep
2) Obtain quests there, one should be about Darkspawn (I don't remember if this was immediate unlock or after something else)
3) Once you clear the Darkspawn, a second part of the quest unlocks to the north, where the poison mists are. You have to inspect an area to unlock a War Room mission to access this area (sorry, forgot the name)
4) Once the area is unlocked, you should be on a mission to investigate the darkspawn. You head up the ridge and you enter Coracavus
5) Complete that area, and this exits you out into the previous locked portion of the map, behind the two locked doors
6) You can now open the doors from the inside
I hope that helps, and again I'm sorry if I'm missing details, but I think I covered the gist of it.