include: Add SPDX identifiers to files missing them

This adds SPDX identifiers to the remaining source files in the
include directory that don't already have them.

Signed-off-by: Martin Roth <martin.roth@amd.corp-partner.google.com>
Change-Id: I0dbf4c839eacf957eb6f272aa8bfa1eeedc0886f
Reviewed-on: https://review.coreboot.org/c/coreboot/+/66501
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/include/cpu/x86/bist.h

@@ -1,3 +1,5 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
 #ifndef CPU_X86_BIST_H
 #define CPU_X86_BIST_H
 

src/include/device/pnp.h

@@ -1,3 +1,5 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
 #ifndef DEVICE_PNP_H
 #define DEVICE_PNP_H