edac, highbank: Fix interrupt setup of mem and l2 controller

Register and enable interrupts after the edac registration. Otherwise
incomming ecc error interrupts lead to crashes during device setup.

Fixing this in drivers for mc and l2.

Signed-off-by: Robert Richter <robert.richter@linaro.org>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Cc: stable <stable@vger.kernel.org>     # 3.6+
Signed-off-by: Robert Richter <rric@kernel.org>