Create Open firmware pseudo driver.

Change ofnet.c to disknet.c and remove almost all ieee1275 specific code.
Create grub_net_malloc to handle iee1275 memory issues in a temporary solution.

net/i386/mem.c

@@ -0,0 +1,10 @@
+#include <grub/types.h>
+#include <grub/err.h>
+#include <grub/misc.h>
+#include <grub/mm.h>
+
+
+void *grub_net_malloc (grub_size_t size)
+{
+  return grub_malloc (size);
+}