volteer: Update servo overlay

Add CCD mode programming for EC.  Remove obsolete jtag_vref controls.

BUG=b:142841233
BRANCH=none
TEST=sudo emerge hdctools
TEST=servod --board=volteer

Change-Id: I91da3c57ae622fa66d59afb70ebd0f955baacb76
Signed-off-by: Keith Short <keithshort@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/hdctools/+/1891751
Reviewed-by: Aseda Aboagye <aaboagye@chromium.org>
Reviewed-by: Nick Vaccaro <nvaccaro@google.com>
diff --git a/servo/servo_interfaces.py b/servo/servo_interfaces.py
index d14a5dd..05492bc 100644
--- a/servo/servo_interfaces.py
+++ b/servo/servo_interfaces.py
@@ -306,6 +306,7 @@
     'sentry',
     'soraka',
     'strago',
+    'volteer',
     'zoombini',
     'zork',
 ]: