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/defaults.sh

@@ -1,24 +1,42 @@
 #!/bin/bash
 
+copy () {
+    rsync -azp -e 'ssh' --exclude '.git' $1 $2
+}
+
+run () {
+    ssh -o "ServerAliveInterval=60" -o "StrictHostKeyChecking no" -t $SERVER $@
+}
+
+run_script () {
+    ssh -o "ServerAliveInterval=60" -o "StrictHostKeyChecking no" -t $SERVER 'bash -s' < $1 "$2"
+}
+
+clean () {
+    # remove remote work dir
+    run "rm -rf $REMOTE_WORK_DIR"
+}
+
 # make parallelism
-CI_MAKE_NPROC=8
+CI_MAKE_NPROC=4
 # chosen based on a 24c system shared with 1 other project
 REMOTE_MAKE_NPROC=4
 
 # verilator version
 VERILATOR_VERSION=v4.034
 
-HOME=$GITHUB_WORKSPACE
+# remote variables
+
 CURRENT_BRANCH=$(git branch --show-current)
 
-# remote variables
 # CI_DIR is defined externally based on the GH repository secret BUILDDIR
 
+HOME=`pwd`
 REMOTE_PREFIX=$CI_DIR/${GITHUB_REPOSITORY#*/}-$CURRENT_BRANCH
-REMOTE_WORK_DIR=$GITHUB_WORKSPACE
-REMOTE_RISCV_DIR=$GITHUB_WORKSPACE/riscv-tools-install
-REMOTE_ESP_DIR=$GITHUB_WORKSPACE/esp-tools-install
-REMOTE_CHIPYARD_DIR=$GITHUB_WORKSPACE
+REMOTE_WORK_DIR=$REMOTE_PREFIX-$GITHUB_SHA-$GITHUB_JOB
+REMOTE_RISCV_DIR=$REMOTE_WORK_DIR/riscv-tools-install
+REMOTE_ESP_DIR=$REMOTE_WORK_DIR/esp-tools-install
+REMOTE_CHIPYARD_DIR=$REMOTE_WORK_DIR/chipyard
 REMOTE_SIM_DIR=$REMOTE_CHIPYARD_DIR/sims/verilator
 REMOTE_FIRESIM_DIR=$REMOTE_CHIPYARD_DIR/sims/firesim/sim
 REMOTE_FPGA_DIR=$REMOTE_CHIPYARD_DIR/fpga