i2c: imc-skylake: add driver for Intel Skylake-X iMC SMBus engine

Add a driver for the integrated memory controller (iMC) SMBus engine on
Intel Skylake-X / Cascade Lake-X processors (socket LGA 2066, platform
X299, PCU function 8086:2085).

The engine provides two SMBus channels — one per pair of DIMM slots —
over which SPD EEPROMs, DDR4 thermal sensors and third-party LED
controllers are accessible. Exposing it as a pair of standard Linux I2C
adapters lets existing tools (i2c-tools, lm-sensors) use it without
bespoke sysfs hacks.

Key design decisions:
- ECAM MMIO access instead of CF8/CFC port I/O (SMM traps port writes)
- Dynamic MCFG table parsing for mmcfg_base (no hardcoding)
- Support for SMBus BYTE_DATA and WORD_DATA transfers
- devm-managed resources with automatic cleanup
- Global mutex to serialize transactions across both channels sharing
  the same ECAM mapping

Signed-off-by: Simone Chifari <simone.chifari@gmail.com>

.github/workflows/ci.yml

@@ -0,0 +1,43 @@
+name: CI
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+    branches:
+      - main
+  workflow_dispatch:
+
+concurrency:
+  group: ci-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install build dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y build-essential linux-headers-$(uname -r)
+
+      - name: Build module
+        run: make
+
+      - name: Run checkpatch
+        run: |
+          curl -sSLo checkpatch.pl https://raw.githubusercontent.com/torvalds/linux/master/scripts/checkpatch.pl
+          curl -sSLo spelling.txt https://raw.githubusercontent.com/torvalds/linux/master/scripts/spelling.txt
+          perl checkpatch.pl --no-tree --strict --no-summary --show-types -f i2c-imc-skylake.c
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: i2c-imc-skylake-${{ github.ref_name }}
+          path: i2c-imc-skylake.ko
+          if-no-files-found: error