ci: Add initial buildkite ci setup

Add setup to utilize buildkite for CI purposes:

1. .buildkite/hooks/pre-command:
   * Handles getting git checkout setup against upstream repo
   * Setup some west module cache (dirs, clean out files & locks)
   * init dir for ccache

2. .buildkite/hooks/post-command:
   * Report disk usage (meant for possible debugging)

3. .buildkite/pipeline.yml [uses to determine what to do]:
   * setup zephyr env vars
   * set which docker container to use
     (export some local disk caches for git, west modules, and ccache)
   * uses plug to general build annotation on failure (junit-annotate)

4. .buildkite/run.sh [ buildkite wrapper to invoke scripts/ci/run.sh ]

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>

.buildkite/hooks/post-command

@@ -0,0 +1,8 @@
+#!/bin/bash
+# Copyright (c) 2020 Linaro Limited
+#
+# SPDX-License-Identifier: Apache-2.0
+
+# report disk usage:
+echo "--- $0 disk usage"
+df -h

.buildkite/hooks/pre-command

@@ -0,0 +1,38 @@
+#!/bin/bash
+# Copyright (c) 2020 Linaro Limited
+#
+# SPDX-License-Identifier: Apache-2.0
+
+# Save off where we started so we can go back there
+WORKDIR=${PWD}
+
+if [ -n "${BUILDKITE_PULL_REQUEST_BASE_BRANCH}" ]; then
+   git fetch -v origin ${BUILDKITE_PULL_REQUEST_BASE_BRANCH}
+   git checkout FETCH_HEAD
+   git config --local user.email "builds@zephyrproject.org"
+   git config --local user.name "Zephyr CI"
+   git merge --no-edit "${BUILDKITE_COMMIT}" || {
+       local merge_result=$?
+       echo "Merge failed: ${merge_result}"
+       git merge --abort
+       exit $merge_result
+   }
+fi
+
+mkdir -p /var/lib/buildkite-agent/zephyr-ccache/
+
+# create cache dirs, no-op if they already exist
+mkdir -p /var/lib/buildkite-agent/zephyr-module-cache/modules
+mkdir -p /var/lib/buildkite-agent/zephyr-module-cache/tools
+mkdir -p /var/lib/buildkite-agent/zephyr-module-cache/bootloader
+
+# Clean cache - if it already exists
+cd /var/lib/buildkite-agent/zephyr-module-cache
+find -type f -not -path "*/.git/*" -not -name ".git" -delete
+
+# Remove any stale locks
+find -name index.lock -delete
+
+# return from where we started so we can find pipeline files from
+# git repo
+cd ${WORKDIR}

.buildkite/pipeline.yml

@@ -0,0 +1,28 @@
+steps:
+  - command:
+    - .buildkite/run.sh
+    env:
+      ZEPHYR_TOOLCHAIN_VARIANT: "zephyr"
+      ZEPHYR_SDK_INSTALL_DIR: "/opt/sdk/zephyr-sdk-0.11.3"
+    parallelism: 20
+    timeout_in_minutes: 120
+    retry:
+      manual: true
+    plugins:
+      - docker#v3.5.0:
+          image: "zephyrprojectrtos/ci:v0.11.8"
+          propagate-environment: true
+          volumes:
+            - "/var/lib/buildkite-agent/git-mirrors:/var/lib/buildkite-agent/git-mirrors"
+            - "/var/lib/buildkite-agent/zephyr-module-cache:/var/lib/buildkite-agent/zephyr-module-cache"
+            - "/var/lib/buildkite-agent/zephyr-ccache:/root/.ccache"
+          workdir: "/workdir/zephyr"
+    agents:
+    - "queue=default"
+
+  - wait: ~
+    continue_on_failure: true
+
+  - plugins:
+      - junit-annotate#v1.7.0:
+          artifacts: sanitycheck-*.xml

.buildkite/run.sh

@@ -0,0 +1,46 @@
+#!/bin/bash
+# Copyright (c) 2020 Linaro Limited
+#
+# SPDX-License-Identifier: Apache-2.0
+
+echo "--- run $0"
+
+git log -n 5 --oneline --decorate --abbrev=12
+
+# Setup module cache
+cd /workdir
+ln -s /var/lib/buildkite-agent/zephyr-module-cache/modules
+ln -s /var/lib/buildkite-agent/zephyr-module-cache/tools
+ln -s /var/lib/buildkite-agent/zephyr-module-cache/bootloader
+cd /workdir/zephyr
+
+export JOB_NUM=$((${BUILDKITE_PARALLEL_JOB}+1))
+
+# ccache stats
+echo ""
+echo "--- ccache stats at start"
+ccache -s
+
+if [ -n "${BUILDKITE_PULL_REQUEST_BASE_BRANCH}" ]; then
+   ./scripts/ci/run_ci.sh  -c -b ${BUILDKITE_PULL_REQUEST_BASE_BRANCH} -r origin \
+	   -m ${JOB_NUM} -M ${BUILDKITE_PARALLEL_JOB_COUNT} -p ${BUILDKITE_PULL_REQUEST}
+else
+   ./scripts/ci/run_ci.sh -c -b ${BUILDKITE_BRANCH} -r origin \
+	   -m ${JOB_NUM} -M ${BUILDKITE_PARALLEL_JOB_COUNT};
+fi;
+
+SANITY_EXIT_STATUS=$?
+
+# Rename sanitycheck junit xml for use with junit-annotate-buildkite-plugin
+mv sanity-out/sanitycheck.xml sanitycheck-${BUILDKITE_JOB_ID}.xml
+buildkite-agent artifact upload sanitycheck-${BUILDKITE_JOB_ID}.xml
+
+# ccache stats
+echo "--- ccache stats at finish"
+ccache -s
+
+# disk usage
+echo "--- disk usage at finish"
+df -h
+
+exit ${SANITY_EXIT_STATUS}

CODEOWNERS

@@ -16,6 +16,7 @@
 /.known-issues/                           @nashif
 /.github/				  @nashif
 /.github/workflows/                       @galak @nashif
+/.buildkite/				  @galak
 /arch/arc/                                @vonhust @ruuddw
 /arch/arm/                                @MaureenHelm @galak @ioannisg
 /arch/arm/core/aarch32/cortex_m/cmse/     @ioannisg