add Digilent HS2 support

Change-Id: If506c33f22d95f4c47f30c4348d461197c976fdd
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/3160
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>

tcl/interface/ftdi/digilent-hs2.cfg

@@ -0,0 +1,10 @@
+# this supports JTAG-HS2 (and apparently Nexys4 as well)
+
+interface ftdi
+ftdi_device_desc "Digilent Adept USB Device"
+ftdi_vid_pid 0x0403 0x6014
+
+ftdi_channel 0
+ftdi_layout_init 0x00e8 0x60eb
+
+reset_config none