autoport: Add GPL boilerplate header to not empty .c files

The idea behind this not to enforce a license on autogenerated code
but is simply out of convenience in the case one wants to make the
result public (in which case it needs to have these license headers).

Change-Id: I1d6b48762b1249bb0becb178a30e1396bf6978fc
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/19510
Reviewed-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Nico Huber <nico.h@gmx.de>

util/autoport/bd82x6x.go

@@ -43,6 +43,7 @@ func (b bd82x6x) GPIO(ctx Context, inteltool InteltoolData) {
 
 	AddROMStageFile("gpio.c", "")
 
+	Add_gpl(gpio)
 	gpio.WriteString("#include <southbridge/intel/common/gpio.h>\n\n")
 
 	addresses := [3][6]int{
@@ -305,6 +306,7 @@ func (b bd82x6x) Scan(ctx Context, addr PCIDevData) {
 	sb := Create(ctx, "early_southbridge.c")
 	defer sb.Close()
 	AddROMStageFile("early_southbridge.c", "")
+	Add_gpl(sb)
 	sb.WriteString(`#include <stdint.h>
 #include <string.h>
 #include <lib.h>
@@ -401,6 +403,7 @@ void mainboard_get_spd(spd_raw_data *spd, bool id_only)
 	gnvs := Create(ctx, "gnvs.c")
 	defer gnvs.Close()
 
+	Add_gpl(gnvs)
 	gnvs.WriteString(`#include <southbridge/intel/bd82x6x/nvs.h>
 
 /* FIXME: check this function.  */