The commit b63128e8 broke the pin muxing
for I2C busses that are enabled from the kernel command line.

Fix this by defining the board registration function omap_register_i2c_bus
in common platform code as it was before but keep the muxing in architecture
dependent files.
Signed-off-by: NJarkko Nikula <jhnikula@gmail.com>
Signed-off-by: NTony Lindgren <tony@atomide.com>