amd64_edac: Fix logic to determine channel for F15 M30h processors

Update current channel selection logic to include F15h, M30h memory
controllers.

Refer F15 M30h BKDG D18F2x110[7:6] (DRAM Controller Select Low)
(Link:http://support.amd.com/TechDocs/49125_15h_Models_30h-3Fh_BKDG.pdf)

Signed-off-by: Aravind Gopalakrishnan <Aravind.Gopalakrishnan@amd.com>
Link: http://lkml.kernel.org/r/1390338216-3873-1-git-send-email-Aravind.Gopalakrishnan@amd.com
Signed-off-by: Borislav Petkov <bp@suse.de>