This allows minidrivers to e.g. hardware accelerate memory
writes.

Same trick as is used for arm7/9 dcc writes.

Added error propagation for memory transfer failures in
code rearrangement.

Also the JTAG end state is not updated until after
the memory write run is complete.
Signed-off-by: Øyvind Harboe <oyvind.harboe@zylin.com>