device, soc: Add SPDX license headers to Makefiles

To help identify the licenses of the various files contained in the
coreboot source, we've added SPDX headers to the top of all of the
.c and .h files. This extends that practice to Makefiles.

Any file in the coreboot project without a specific license is bound
to the license of the overall coreboot project, GPL Version 2.

This patch adds the GPL V2 license identifier to the top of all
makefiles in the device and soc directories that don't already have an
SPDX license line at the top.

Signed-off-by: Martin Roth <gaumless@gmail.com>
Change-Id: I89c05c7c1c39424de2e3547c10661c7e3f58b8f7
Reviewed-on: https://review.coreboot.org/c/coreboot/+/76951
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Reviewed-by: Tim Crawford <tcrawford@system76.com>

src/device/Makefile.inc

@@ -1,3 +1,5 @@
+## SPDX-License-Identifier: GPL-2.0-only
+
 ramstage-y += device.c
 ramstage-y += root_device.c
 ramstage-y += cpu_device.c

src/soc/amd/common/block/xhci/Makefile.inc

@@ -1,2 +1,4 @@
+## SPDX-License-Identifier: GPL-2.0-only
+
 ramstage-$(CONFIG_SOC_AMD_COMMON_BLOCK_XHCI)    += xhci.c
 smm-$(CONFIG_SOC_AMD_COMMON_BLOCK_XHCI_ELOG)    += elog.c

src/soc/intel/common/block/vtd/Makefile.inc

@@ -1,3 +1,5 @@
+## SPDX-License-Identifier: GPL-2.0-only
+
 # VT-d will not be functional in bootblock and verstage yet.
 # It will become available after FSP memory init.
 # If coreboot does native VT-d initialization, early DMA protection