i2c-piix4: Add AMD SB900 SMBus device ID

Add new SMBus device ID for AMD SB900.

Signed-off-by: Crane Cai <crane.cai@amd.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>
diff --git a/Documentation/i2c/busses/i2c-piix4 b/Documentation/i2c/busses/i2c-piix4
index f889481..c5b37c5 100644
--- a/Documentation/i2c/busses/i2c-piix4
+++ b/Documentation/i2c/busses/i2c-piix4
@@ -8,6 +8,8 @@
     Datasheet: Only available via NDA from ServerWorks
   * ATI IXP200, IXP300, IXP400, SB600, SB700 and SB800 southbridges
     Datasheet: Not publicly available
+  * AMD SB900
+    Datasheet: Not publicly available
   * Standard Microsystems (SMSC) SLC90E66 (Victory66) southbridge
     Datasheet: Publicly available at the SMSC website http://www.smsc.com