qdev/isa: convert ne2000

Also split the isa bits into a separate source file, so we don't drag in
a dependency for isa-bus.o for machines which want ne2k_pci only.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
diff --git a/hw/pc.c b/hw/pc.c
index e1ffaa4..9497f71 100644
--- a/hw/pc.c
+++ b/hw/pc.c
@@ -1052,7 +1052,7 @@
     if (nb_ne2k == NE2000_NB_MAX)
         return;
     isa_ne2000_init(ne2000_io[nb_ne2k],
-                    isa_reserve_irq(ne2000_irq[nb_ne2k]), nd);
+                    ne2000_irq[nb_ne2k], nd);
     nb_ne2k++;
 }