[RFA]: Fix partial memory transfers

[Andrew Cagney]

"J.T. Conklin" wrote:
> 
> I submit the enclosed patch to target.c for approval.
> 
> My recent commit to move the dcache on top of the target xfer_memory
> vector introduced a bug such that target_partial_xfer_memory() would
> always perform a complete transfer, which defeated the entire purpose
> of that function.
> 
> The enclosed patch fixes do_xfer_memory(), the low-level function that
> calls the xfer_memory vector function(s), to perform only one transfer.
> The dcache already has the logic that will call do_xfer_memory multiple
> times if it returns a partial transfer.
> 
> This patch also fixes up comments for the *xfer_memory* functions.
> Some have been wrong/misleading for a very long time.
> 
> This patch also includes a bug fix from Nick, which caused me to look
> at and fine the above bug.  I'm including it in this patch because he
> retracted the bug fix when I mentioned this patch was coming.

Yes, ok by me.

	Andrew