Move Chipyard CI to Github Actions

- As similar as possible to the circle ci code.
- The `.github/README.md` file has a fair amount of documentation for this.
- Creates a worfklow file
  - re-uses most of the circleci/scipts unchanged
  - defines a number of *Composite Actions* which are like YML subroutines
- Removes the circle-ci code
- Points the CI badge in the top level README to use the GA test result

.github/scripts/install-verilator.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+
+# move verilator to the remote server
+
+# turn echo on and error on earliest command
+set -ex
+
+# get shared variables
+SCRIPT_DIR="$( cd "$( dirname "$0" )" && pwd )"
+source $SCRIPT_DIR/defaults.sh
+
+# clean older directories (delete prior directories related to this branch also)
+run_script $LOCAL_CHIPYARD_DIR/.github/scripts/clean-old-files.sh $CI_DIR
+run "rm -rf $REMOTE_PREFIX*"
+
+# set stricthostkeychecking to no (must happen before rsync)
+run "echo \"Ping $SERVER\""
+
+run "git clone http://git.veripool.org/git/verilator $REMOTE_VERILATOR_DIR; \
+     cd $REMOTE_VERILATOR_DIR; \
+     git checkout $VERILATOR_VERSION; \
+     autoconf; \
+     export VERILATOR_ROOT=$REMOTE_VERILATOR_DIR; \
+     ./configure; \
+     make -j$REMOTE_MAKE_NPROC;"