Auto-select JTAG transport when appropriate

Auto-select JTAG transport when appropriate

I looked through all the target configs after stripping comments and
such from them with sed to see what jtag-specific commands can appear
first, and it looks like all the meaningful combinations should be
covered.

Change-Id: I8d543407b7f4ac8aca7354ecd50e841c8a04d5f3
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/2179
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>