Now I can issue "reset halt" and have everything act smoothly;
the vector_catch hardware is obviously not kicking in, but the
rest of the reset sequence acts sanely.

 - TAP "setup" event enables the DAP, not omap3_dbginit
   (resolving a chicken/egg bug I noted a while back)
 - Remove stuff from omap3_dbginit which should never be
   used in event handlers
 - Cope better with slow clocking during reset

Also, stop hard-wiring the target name: use the input params in
the standard way, and set up $_TARGETNAME as an output param.

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