i2c-nforce2: Add support for MCP67, MCP73, MCP78S and MCP79

The MCP78S and MCP79 appear to be compatible with the previous nForce
chips as far as the SMBus controller is concerned. The MCP67 and MCP73
were not tested yet but I'd be very surprised if they weren't
compatible too.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Oleg Ryjkov <olegr@olegr.ca>
Cc: Malcolm Lalkaka <mlalkaka@gmail.com>
Cc: Zbigniew Luszpinski <zbiggy@o2.pl>