acpi: Reserve hardware IDs for custom Intel GMBus I2C driver

GMBus is an I2C compatible link on Intel IGPUs. Most non-Linux OS's
don't support accessing this ordinarily, so a custom driver is
needed with a bit of ACPI hackery. Reserve 2 IDs from the
coreboot namespace so that the 2 devices required can be populated
in Windows device manager

Change-Id: I389612441e96ce2fc5e006051e523661953eba6e
Signed-off-by: CoolStar <coolstarorganization@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76413
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Lean Sheng Tan <sheng.tan@9elements.com>

src/include/acpi/acpi.h

@@ -68,6 +68,8 @@ enum acpi_device_sleep_states {
 /* List of ACPI HID that use the coreboot ACPI ID */
 enum coreboot_acpi_ids {
 	COREBOOT_ACPI_ID_CBTABLE	= 0x0000, /* BOOT0000 */
+	COREBOOT_ACPI_ID_IGD_GMBUS_ARB  = 0x0001, /* BOOT0001 */
+	COREBOOT_ACPI_ID_IGD_GMBUS_LINK = 0x0002, /* BOOT0002 */
 	COREBOOT_ACPI_ID_MAX		= 0xFFFF, /* BOOTFFFF */
 };