jtag: add connect_type reset_config mode flag

jtag: add connect_type reset_config mode flag

This adds the ability to request to the adapter how we want to connect to
the target, eg. while srst is asserted or not.

This ability can very handy for connecting to unresponsive targets.
A prerequisite is that the target supports srst_nogate.

Change-Id: I0f7c9475160048e8a963e16077754f5403ac8325
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/976
Reviewed-by: Paul Fertser <fercerpav@gmail.com>
Tested-by: jenkins
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>