bd82x6x: Move common bd82x6x S3 detect to bd82x6x code.

Change-Id: I9ba1fa5f9ad38cb619466c6199eacd219bc53281
Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-on: http://review.coreboot.org/6921
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <pgeorgi@google.com>