[PATCH] rewrite i2c-amd756 to resemble a linux driver

This is a large rewrite of i2c-amd756 (added by Pavel post 2.5.53
although it's not his code) into a driver following linux driver
guide lines.  As a side-effect it shrinks the driver by almost one
fifth.  Tested with an early AMD756-based board.

 - use proper PCI API
 - use pr_debug instead of #ifdef DEBUG mess
 - use named initializers
 - completly restructure init/exit code
 - mark everything static