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

.circleci/create-hash.sh

@@ -1,23 +0,0 @@
-#!/bin/bash
-
-# get the hash of riscv-tools
-
-# turn echo on and error on earliest command
-set -ex
-set -o pipefail
-
-# get shared variables
-SCRIPT_DIR="$( cd "$( dirname "$0" )" && pwd )"
-source $SCRIPT_DIR/defaults.sh
-
-# enter bhd repo
-cd $LOCAL_CHIPYARD_DIR
-
-# Use normalized output of git-submodule status as hashfile
-for tools in 'riscv-tools' 'esp-tools' ; do
-    git submodule status "toolchains/${tools}" 'toolchains/libgloss' 'toolchains/qemu' |
-    while read -r line ; do
-        echo "${line#[!0-9a-f]}"
-    done > "${HOME}/${tools}.hash"
-done
-echo "Hashfile for riscv-tools and esp-tools created in $HOME"