Patch from Deepak Saxena

Latest (and hopefully last :) patch for generic DMA buffer bouncing.

- Fixed SA1111 dma_needs_bounce
- Added check for out of bounds buffers.
- Made dmabounce.c directly implement dma_* API

Note that I didn't do the following:

#ifndef CONFIG_DMABOUNCE
inline implementations of all functions
#else
extern declarations
#endif

Instead I wrapped it individual in #ifndef/#else blocks to keep the
comments in the same area as function declarations.  IMHO this makes 
it easier for someone to go look at the comments if they need to know 
what a specific API does.