ADIv5: remove ATOMIC/COMPOSITE interface mode

ADIv5: remove ATOMIC/COMPOSITE interface mode

This removes context-sensitivity from the programming interface and makes
it possible to know what a block of code does without needing to know the
previous history (specifically, the DAP's "trans_mode" setting).

The mode was only set to ATOMIC briefly after DAP initialization, making
this patch be primarily cleanup; almost everything depends on COMPOSITE.
The transactions which shouldn't have been queued were already properly
flushing the queue.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>