edac: altera: Add Altera SDRAM EDAC support

edac: altera: Add Altera SDRAM EDAC support

This patch adds support for the CycloneV and ArriaV SDRAM controllers.
Correction and reporting of SBEs, Panic on DBEs.

There was a discussion thread on whether this driver should be an mfd driver
or just make use of syscon, which is already a mfd. Ultimately, the
decision to use a simple syscon interface was reached.[1]

[1] https://lkml.org/lkml/2014/7/30/514

[dinguyen] Fixed Kconfig to have EDAC_ALTERA_MC as a tristate to prevent a
build failure for allmodconfig.

Signed-off-by: Thor Thayer <tthayer@opensource.altera.com>
Acked-by: Borislav Petkov <bp@suse.de>
[dinguyen] cleaned up commit message
Signed-off-by: Dinh Nguyen <dinguyen@opensource.altera.com>