In light of your reiteration that you're asking specifically about EL, I agree that it ought to be 7. Any encounter which includes the threat of facing a CR7 creature ought to be considered that EL, IMO.
Given the game mechanics, though, I think the question of CR and experience awards is a much more interesting one. This is a bit of a philosophical argument (i.e. unsupported by the rules), as it's been over a year since I've actually read my DMG, and even that was 3.0.
I've always felt that a trap that may or may not cause you to fight monsters should have a much lower CR than just placing the monster. If just facing a mini-efreet that's guaranteed to be there is CR7, then why wouldn't adding a straightforward way to bypass the encounter reduce the CR for the encounter? Overcoming a challenge which MAY result in a CR7 is less risky than actually facing a CR7 encounter. If the efreet does appear, then of course the PCs should receive the appropriate award for facing a CR7 challenge, but if they bypass it by magic or by disarming a trap, they never really faced the kind of risk posed by a CR7 encounter, and their reward should be reduced accordingly. Also, what if they tunneled through underneath the prison without ever even discovering the trap was there? Technically they "overcame" the challenge, but completely unwittingly and with zero risk to themselves. In this case, I don't think they should get anything -- just as if they had gone down an alternate corridor which reached the same destination but without challenges.