amd64_edac: Add support for F15h DCT PCI config accesses

amd64_edac: Add support for F15h DCT PCI config accesses

F15h "multiplexes" between the configuration space of the two DRAM
controllers by toggling D18F1x10C[DctCfgSel] while F10h has a different
set of registers for DCT0, and DCT1 in extended PCI config space.

Add DCT configuration space accessors per family thus wrapping all the
different access prerequisites. Clean up code while at it, shorten
names.

Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>