Initial PnP bios call support.

This commit provides just enough PnP support for gPXE to not hook int19.
diff --git a/src/post.c b/src/post.c
index b286826..f55d53d 100644
--- a/src/post.c
+++ b/src/post.c
@@ -198,6 +198,7 @@
     memmap_setup();
     ram_probe();
 
+    pnp_setup();
     vga_setup();
 
     kbd_setup();