github: workflows: Add upstream build workflow

Add a workflow to verify that it's possible to fetch the Silabs HAL tree
and to build a Bluetooth sample agains a Silabs board using the latest
upstream main tree. Run the workflow at 5:15 UTC every day.

Signed-off-by: Johan Hedberg <[email protected]>

.github/workflows/upstream-build.yml

@@ -0,0 +1,54 @@
+name: Silabs upstream daily build
+
+on:
+  pull_request:
+    types:
+    - edited
+    - opened
+    - reopened
+    - synchronize
+    #schedule:
+    #- cron: "15 5 * * *"
+
+jobs:
+  build:
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-22.04, macos-14, windows-2022]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+        with:
+          path: zephyr-silabs
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: 3.11
+
+      - name: Install Silabs-specific python dependencies
+        run: |
+          pip3 install crc
+
+      - name: Setup Zephyr project
+        uses: zephyrproject-rtos/action-zephyr-setup@v1
+        with:
+          app-path: zephyr-silabs
+        toolchains: arm-zephyr-eabi
+
+      - name: Update manifest to point at upstream main branch
+        working-directory: zephyr-silabs
+        shell: bash
+        run: |
+          Z_REV=`grep -A 2 'name: zephyr$' west.yml|grep revision:|sed 's/^.*revision: //'`
+          sed -i .orig s/$Z_REV/main/ west.yml
+          west update
+          west blobs fetch hal_silabs
+
+      - name: Build Bluetooth sample for xG27
+        working-directory: zephyr-silabs
+        shell: bash
+        run: |
+          west build -b xg27_dk2602a/efr32bg27c140f768im40 ../zephyr/samples/bluetooth/peripheral_hr