[skge] Add driver for skge NICs

This code is based on the linux skge driver. It supports Marvell Yukon
and SysKonnect Gigabit chipsets.

The code is based on code Michael Decker <mrd999@gmail.com> wrote for
Google Summer of Code 2008.

Support for dual-port cards is untested. The code, however, was left
in. In my opinion it's easier to fix the code if we need to, instead
of having to add support for it from scratch.

Signed-off-by: Marty Connor <mdc@etherboot.org>

src/include/gpxe/errfile.h

 #define ERRFILE_atl1e		     ( ERRFILE_DRIVER | 0x00510000 )
 #define ERRFILE_sis190		     ( ERRFILE_DRIVER | 0x00520000 )
 #define ERRFILE_myri10ge	     ( ERRFILE_DRIVER | 0x00530000 )
+#define ERRFILE_skge		     ( ERRFILE_DRIVER | 0x00540000 )
 
 #define ERRFILE_scsi		     ( ERRFILE_DRIVER | 0x00700000 )
 #define ERRFILE_arbel		     ( ERRFILE_DRIVER | 0x00710000 )