Make ADIv5 internals use the two new transport-neutral calls for reading
and writing DP registers; and do the same for external callers.  Also,
bugfix some of their call sites to handle the fault returns, instead of
ignoring them.

Remove most of the JTAG-specific calls, using their code as the bodies
of the JTAG-specific implementation for the new methods.

NOTE that there's a remaining issue:  mem_ap_read_buf_u32() makes calls
which are JTAG-specific.  A later patch will need to remove those, so
JTAG-specific operations can be removed from this file, and so that SWD
support will be able to properly drop in as just a transport layer to the
ADIv5 infrastructure.  (The way read results are posted may need some more
attention in the transport-neutrality interface.)

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