[pci] Enable memory cycles in adjust_pci_device()

adjust_pci_device() has historically enabled bus-mastering and I/O
cycles, but has never previously needed to enable memory cycles.  Some
EFI systems seem not to enable memory cycles by default, so add that
to the list of PCI command register bits that we force on.

src/drivers/bus/pci.c

 	unsigned char pci_latency;
 
 	pci_read_config_word ( pci, PCI_COMMAND, &pci_command );
-	new_command = pci_command | PCI_COMMAND_MASTER | PCI_COMMAND_IO;
+	new_command = ( pci_command | PCI_COMMAND_MASTER |
+			PCI_COMMAND_MEM | PCI_COMMAND_IO );
 	if ( pci_command != new_command ) {
 		DBG ( "PCI BIOS has not enabled device %02x:%02x.%x! "
 		      "Updating PCI command %04x->%04x\n", pci->bus,