Patch from Lennert Buytenhek

It's silly to have I2C enabled in all ixp2000 defconfigs but not to
have the ixp2000 bus driver enabled in any of them.  This patch enables
CONFIG_I2C_IXP2000 for all in-tree ixp2000 boards.
Signed-off-by: NLennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: NDeepak Saxena <dsaxena@plexity.net>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>