soc/amd: factor out SMBUS controller registers into common header

The patch also rewrites the bit definition using shifts to make them
easier to read.

The older non-SoC chips can probably also use the new header file, but
for this patch the scope is limited to soc/amd, since the older non-SoC
chips don't use the SMBUS controller code in soc/amd/common.

TEST=Timeless build for amd/mandolin and amd/gardenia doesn't change.

Change-Id: Ifd5e7e64a41f1cb20cdc4d6ad1e675d7f2de352b
Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/48188
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>

src/soc/amd/stoneyridge/southbridge.c

@@ -17,6 +17,7 @@
 #include <amdblocks/acpimmio.h>
 #include <amdblocks/lpc.h>
 #include <amdblocks/acpi.h>
+#include <amdblocks/smbus.h>
 #include <soc/southbridge.h>
 #include <soc/smi.h>
 #include <soc/amd_pci_int_defs.h>