jtag: Rewrite TAP verification/auto-probe logic

jtag: Rewrite TAP verification/auto-probe logic

Enable auto-creating additional discovered TAPs even if some TAPs are
predefined, avoiding initialization failure when it's not necessary.

Also, drop the arbitrary limit on the number of predefined TAPs. Still,
don't auto-create any if there are more than 20 TAPs already, to stop
a noisy connection from creating unlimited TAPs.

Create auto-probed TAPs with less noise.

Reduce code duplication between verification and auto-probing.

Change-Id: I82a504d92dbcc0060206e71f10c5158256b5f561
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/2236
Tested-by: jenkins
Reviewed-by: Paul Fertser <fercerpav@gmail.com>