[U-Boot] DMA bounce buffer in FAT code

[Jean-Jacques Hiblot]

Hi all,

commits 8133f43d and cc63b25e introduced buffer bouncing at the level of 
the FAT fs driver. I came across those because of printf() saying that 
the buffer is not aligned when I save my env in file on a FAT partition. 
Those messages are annoying because they lead to think that there's a 
problem when saving the environment. We could move them to debug() or at 
least indicate that's only a warning.

However I think that removing the bounce buffer mechanism altogether is 
better option. The alignment constraint doesn't belong at this level and 
indeed there are controllers that do not require it at all (those not 
using DMA for once). It could be moved to the block level and activated 
only if the driver for the controller needs it. Or it could be left to 
the driver of the controller do implement it.

I'm willing to prepare the patches for the modifications if you think 
they make sense.

Jean-Jacques