i2c: Obsolete i2c-ixp2000, i2c-ixp4xx and scx200_i2c

The new generic i2c-gpio driver should be used instead.
The obsolete drivers will be removed in September 2007.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
Cc: Deepak Saxena <dsaxena@plexity.net>
Cc: Jordan Crouse <jordan.crouse@amd.com>