add support for more i2c muxes

This patch should bring support for several kernel modules related to
I2C to openwrt, which are existing for several years now. Namely there
is the i2c-tiny-usb bus driver, to hook up an I2C bus on any device with
usb support (prevent voiding warranty when opening and soldering).
Second, there is support for the i2c-mux driver and pca954x as a I2C
switch driver.
Finally there is support for common I2C gpio expander driver modules
pca953x and pcf857x. They work without providing platform data recently
(can be instantiated at runtime).

Signed-off-by: Hartmut Knaack <knaack.h@gmx.de>

SVN-Revision: 28334