[U-Boot] new "dataflash_mmc_mux" command in u-boot-at91.git

[Ulf Samuelsson]

This command will allow the user to select if the 
SD-card controller (mci) or the SPI is available on 
the Multimedia card connector on the at91rm9200ek/dk.

I think that the name is a little too specific
and would like to have it changed to a more generic name.

Today, we only have it for these boards, and muxing 
functionality is the same on both boards.

It is possible that other board manufacturers
would like to be able to multiplex two other functions

Using "io" or "mux" or similar would be much more generic with
a user interface of

io [ pin ] [low_value | high_value ]

If the value is uniquely allocated to a pin,
then supplying the pin name is really not neccessary.

Best Regards
Ulf Samuelsson