EDAC, altera: Add register offset for ECC Enable

EDAC, altera: Add register offset for ECC Enable

In preparation for the Arria10 peripheral ECCs, add a register offset
from the ECC base to index to the ECC enable register.

Signed-off-by: Thor Thayer <tthayer@opensource.altera.com>
Cc: devicetree@vger.kernel.org
Cc: dinguyen@opensource.altera.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux@arm.linux.org.uk
Cc: linux-edac <linux-edac@vger.kernel.org>
Link: http://lkml.kernel.org/r/1459450087-24792-3-git-send-email-tthayer@opensource.altera.com
Signed-off-by: Borislav Petkov <bp@suse.de>