[legal] Add a selection of FILE_LICENCE declarations

Add FILE_LICENCE declarations to almost all files that make up the
various standard builds of gPXE.

src/arch/i386/interface/syslinux/com32_call.c

@@ -21,6 +21,8 @@
  *
  */
 
+FILE_LICENCE ( GPL2_OR_LATER );
+
 #include <stdint.h>
 #include <realmode.h>
 #include <comboot.h>

src/arch/i386/interface/syslinux/com32_wrapper.S

@@ -16,6 +16,8 @@
  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+FILE_LICENCE ( GPL2_OR_LATER )
+
 	.text
 	.arch i386
 	.code32

src/arch/i386/interface/syslinux/comboot_call.c

@@ -21,6 +21,8 @@
  *
  */
 
+FILE_LICENCE ( GPL2_OR_LATER );
+
 #include <errno.h>
 #include <realmode.h>
 #include <biosint.h>

src/arch/i386/interface/syslinux/comboot_resolv.c

@@ -5,6 +5,8 @@
 #include <gpxe/process.h>
 #include <gpxe/resolv.h>
 
+FILE_LICENCE ( GPL2_OR_LATER );
+
 static int comboot_resolv_rc;
 static struct in_addr comboot_resolv_addr;