4-bit SD Card mode

[Björn König]

Hello,

I think lot of you know the message 'Setting controller bus width to 1' in
conjunction with AT91 SD Card interfaces. I'd like to suggest to disable
this message in src/arm/at91/at91_mci.c for two reasons: 1) it occurs
excessively and 2) there is no useful information content with this
message. Since it is improbable that the driver ever supports the 4-bit
mode we also don't need to be informed whether we use 1-bit or 4-bit mode.
It is improbable (unless somebody is already working on it) because the
4-bit mode requires either polling or a very special interrupt handling
that is not covered by the publicly available simplified SD Card
specifications.

Regards
Björn