This patch adds support for multiple I2C busses on the PPC4xx
platforms. Define CONFIG_I2C_MULTI_BUS in the board config file
to make use of this feature.

It also merges the 405 and 440 i2c header files into one common
file 4xx_i2c.h.

Also the 4xx i2c reset procedure is reworked since I experienced
some problems with the first access on the 440SPe Katmai board.

Signed-off-by: Stefan Roese <sr@denx.de>