[phantom] Do not halt PEGs on driver shutdown

Halting the PEGs breaks platforms where there is sideband access to
the NIC (e.g. HP machines using iLO).  (We have to retain the
unhalting code because on some other platforms (e.g. IBM blades with
BOFM) the pre-PXE firmware must halt the PEGs to avoid issues with the
BIOS rereading via the expansion ROM BAR.)

src/drivers/net/phantom/phantom.c

 	return 0;
 }
 
-/**
- * Halt all PEGs
- *
- * @v phantom		Phantom NIC
- */
-static void phantom_halt_pegs ( struct phantom_nic *phantom ) {
-	phantom_writel ( phantom, 1, UNM_PEG_0_HALT );
-	phantom_writel ( phantom, 1, UNM_PEG_1_HALT );
-	phantom_writel ( phantom, 1, UNM_PEG_2_HALT );
-	phantom_writel ( phantom, 1, UNM_PEG_3_HALT );
-	phantom_writel ( phantom, 1, UNM_PEG_4_HALT );
-}
-
 /**
  * Unhalt all PEGs
  *
  err_check_boot_enable:
  err_init_rcvpeg:
  err_init_cmdpeg:
-	phantom_halt_pegs ( phantom );
  err_map_crb:
 	netdev_nullify ( netdev );
 	netdev_put ( netdev );
 
 	unregister_settings ( &phantom->settings );
 	unregister_netdev ( netdev );
-	phantom_halt_pegs ( phantom );
 	netdev_nullify ( netdev );
 	netdev_put ( netdev );
 }