drivers: edac: Fix error code parsing and initial check for bus errors

Primary error code reporting is out of sync with latest documentation.
Update the error values to properly reflect what is listed. Further add
an initial check for bus errors before reporting any uncorrectable error
so that it will not be confused for an ECC error.

Change-Id: If5e6adee3420751e8ad399c57568985fc63bf66c
Signed-off-by: Kyle Yan <kyan@codeaurora.org>