i2c-piix4: Support AMD auxiliary SMBus controller

Some AMD chipsets, such as the SP5100, have an auxiliary SMBus
controller with a second set of registers. This patch adds
support for this auxiliary controller.

Tested on ASUS KCMA-D8 motherboard.

Signed-off-by: Andrew Armenia <andrew@asquaredlabs.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
index 7244c8b..2e7530a 100644
--- a/drivers/i2c/busses/Kconfig
+++ b/drivers/i2c/busses/Kconfig
@@ -133,7 +133,7 @@
 	    ATI IXP300
 	    ATI IXP400
 	    ATI SB600
-	    ATI SB700
+	    ATI SB700/SP5100
 	    ATI SB800
 	    AMD Hudson-2
 	    Serverworks OSB4
@@ -143,6 +143,10 @@
 	    Serverworks HT-1100
 	    SMSC Victory66
 
+	  Some AMD chipsets contain two PIIX4-compatible SMBus
+	  controllers. This driver will attempt to use both controllers
+	  on the SB700/SP5100, if they have been initialized by the BIOS.
+
 	  This driver can also be built as a module.  If so, the module
 	  will be called i2c-piix4.