PXE: Use consistent naming for PXE ROMs

And add missing ROMs to tarbin build target.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
diff --git a/hw/ne2000.c b/hw/ne2000.c
index 5966359..b668ad1 100644
--- a/hw/ne2000.c
+++ b/hw/ne2000.c
@@ -742,7 +742,7 @@
     if (!pci_dev->qdev.hotplugged) {
         static int loaded = 0;
         if (!loaded) {
-            rom_add_option("pxe-ne2k_pci.bin", -1);
+            rom_add_option("pxe-ne2k_pci.rom", -1);
             loaded = 1;
         }
     }