or1k_du_adv: some cleanup, malloced field and retval
or1k_du_mohor: improve speed while using usb_blaster

usb_blaster does not like to have in and out transfert
in a single jtag_add_dr_scan (?!?). So split in and out
fields in or1k_jtag_mohor_debug_write_go to improve speed.
or1k_du_adv: remove redundant jtag_execute_queue