This partially corrects an inappropriate name choice (and its
associated FIXME).
There are still too many variables named "swjdp", bug little
current code actually relies on them referencing an SWJ-DP instead
of some other flavor of DAP. Only the two new dap_to{swd,jtag}()
calls could behave differently on an SWJ-DP instead of a SW-DP or
a JTAG-DP.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>