Add ERRFILE information for e1000_main and e1000_hw, part of the new e1000 driver

It is likely we will rename e1000_main to e1000 when the new e1000 driver is debugged.

src/include/gpxe/errfile.h

 #define ERRFILE_via_velocity	     ( ERRFILE_DRIVER | 0x00450000 )
 #define ERRFILE_w89c840		     ( ERRFILE_DRIVER | 0x00460000 )
 #define ERRFILE_ipoib		     ( ERRFILE_DRIVER | 0x00470000 )
+#define ERRFILE_e1000_main	     ( ERRFILE_DRIVER | 0x00480000 )
+#define ERRFILE_e1000_hw	     ( ERRFILE_DRIVER | 0x00490000 )
 
 #define ERRFILE_scsi		     ( ERRFILE_DRIVER | 0x00700000 )
 #define ERRFILE_arbel		     ( ERRFILE_DRIVER | 0x00710000 )