Add a new JTAG "setup" event; use for better DaVinci ICEpick support.

The model is that this fires after scanchain verification, when it's
safe to call "jtag tapenable $TAPNAME".  So it will fire as part of
non-error paths of "init" and "reset" command processing.  However it
will *NOT* trigger during "jtag_reset" processing, which skips all
scan chain verification, or after verification errors.

ALSO:
 - switch DaVinci chips to use this new mechanism
 - log TAP activation/deactivation, since their IDCODEs aren't verified
 - unify "enum jtag_event" scripted event notifications
 - remove duplicative JTAG_TAP_EVENT_POST_RESET


git-svn-id: svn://svn.berlios.de/openocd/trunk@2800 b42882b7-edfa-0310-969c-e2dbd0fdcd60