Add VEA unittest to the building list of devices with video encoder.

There are some devices will have video encoder on it, and we will need to
test these video encoder. We have check the building flags of some devices
and find proper flags for adding video encode accelerator unittest to
the build list.

Run the default tests on the device.

Bug: b/129457839
Test: Rebuild the image and check if the binary exists.
Change-Id: I5133b65573edc7a8137244c163d0baefd5632201
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1712442Reviewed-by: Yuchen Liu <yucliu@chromium.org>
Commit-Queue: Jyun-jhe Chou <hobexd@google.com>
Cr-Commit-Position: refs/heads/master@{#681148}

chromecast/BUILD.gn

@@ -86,6 +86,14 @@ cast_test_group("cast_tests") {
     }
   }
 
+  if (use_v4l2_codec && enable_video_capture_service) {
+    tests += [ "//media/gpu:video_encode_accelerator_unittest" ]
+  }
+
+  if (use_v4l2_codec) {
+    tests += [ "//media/gpu:video_decode_accelerator_unittest" ]
+  }
+
   if (is_linux) {
     tests += [
       "//chromecast/crash:cast_crash_unittests",