Your game should auto-register. If it doesn't:
How to Import Your World State from the Dragon Age Keep into Dragon Age: Inquisition for how to tell if they are linked from within the Keep instead.
If your games are not showing up as being registered on the Old BSN and you are on a console and have played while online, your Origin and console accounts might not be linked.
This can happen if you did not use the same email address for both accounts, have always played offline, or if you first linked/registered while syncing was down during Keep development.
Any games registered to you will show up in the "My Games" menu on the left side of the Old BSN, and in the "Games Registered to.." section on the Player Profiles page (My Games > Player Profiles).
To see if your Origin and XBox Gamertag / PSN ID are linked:
Either log into the BSN and go to User Entitlements here: https://social.bioware.com/user_entitlements.php
(It will show your Origin account associations at the top)
If (1) your console account is not listed, or (2) if it is, but there is nothing listed in the BSN site menu in the "My Games" menu under Player Profiles or "Games Registered to.." section on the Player Profiles page, then link the two via Origin:
Once imported, this will link your accounts. Dragon Age: Origins should eventually show up under the "My Games" menu on the BSN web site and under "Games Registered to.." on the Player Profiles page.