jlink: add jlink_pid to specify the pid to use

this will allow us to use multiple jlink at the same time as when
the USB-Address is specified the PID change from 0x0101 to
(0x101 + usb_adress)

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>

doc/openocd.texi

@@ -2323,6 +2323,8 @@ Segger jlink USB adapter
 @c     dumps status
 @c command:	jlink hw_jtag (2|3)
 @c     sets version 2 or 3
+@c command:	 jlink pid
+@c     set the pid of the interface we want to use
 @end deffn
 
 @deffn {Interface Driver} {parport}