[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/drivers/bus/eisa.c

@@ -7,6 +7,8 @@
 #include <unistd.h>
 #include <gpxe/eisa.h>
 
+FILE_LICENCE ( GPL2_OR_LATER );
+
 static void eisabus_remove ( struct root_device *rootdev );
 
 /**

src/drivers/bus/isa.c

@@ -6,6 +6,8 @@
 #include <gpxe/io.h>
 #include <gpxe/isa.h>
 
+FILE_LICENCE ( GPL2_OR_LATER );
+
 /*
  * isa.c implements a "classical" port-scanning method of ISA device
  * detection.  The driver must provide a list of probe addresses

src/drivers/bus/isapnp.c

@@ -55,6 +55,8 @@
  *
  */
 
+FILE_LICENCE ( GPL2_OR_LATER );
+
 #include <stdint.h>
 #include <stdlib.h>
 #include <string.h>

src/drivers/bus/mca.c

@@ -5,6 +5,8 @@
  *
  */
 
+FILE_LICENCE ( BSD2 );
+
 #include <stdint.h>
 #include <string.h>
 #include <stdlib.h>

src/drivers/bus/pci.c

@@ -19,6 +19,8 @@
  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  */
 
+FILE_LICENCE ( GPL2_OR_LATER );
+
 #include <stdint.h>
 #include <stdlib.h>
 #include <stdio.h>

src/drivers/bus/pciextra.c

@@ -1,3 +1,5 @@
+FILE_LICENCE ( GPL2_OR_LATER );
+
 #include <stdint.h>
 #include <gpxe/pci.h>