swj-dp.tcl (SWD infrastructure #1)

Provide new helper proc that can set up either an SWD or JTAG DAP
based on the transport which is in use -- mostly for SWJ-DP.

 Also update some SWJ-DP based chips/targets to use it.  The goal
is making SWD-vs-JTAG transparent in most places.  SWJ-DP based chips
really need this flexible configuration to cope with debug adapters
that support different transports, without needing new target configs
for each transport or adapter.

For JTAG-DP, callers will use "jtag newtap" directly, as today; only
one chip-level transport option exists.

For SW-DP (e.g. LPC1[13]xx or EFM32, they'll use "swd newdap" directly
(part of an upcoming SWD transport patch).  Again, only one transport
option exists, so hard-wiring is appropriate there.

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