soc/intel/alderlake: Hook up GMA ACPI brightness controls

Add function needed to generate ACPI backlight control SSDT, along with
Kconfig values for accessing the registers.

Tested by adding gfx register on system76/lemp11. Backlight controls
work on Windows 10 and Linux 6.1.

Change-Id: I1cc33bf0121ff44aea68a7e3615c5e58e2ab6ce2
Signed-off-by: Tim Crawford <tcrawford@system76.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/69076
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/soc/intel/alderlake/graphics.c

@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+
+#include <intelblocks/graphics.h>
+#include <soc/ramstage.h>
+
+const struct i915_gpu_controller_info *
+intel_igd_get_controller_info(const struct device *const dev)
+{
+	const struct soc_intel_alderlake_config *const chip = dev->chip_info;
+	return &chip->gfx;
+}