Changes to fix bad DMA handling by disk when using scatter gather page

mappings (writes still unverified, and read could probably be looked over
a bit more too)

dev/ide_disk.cc:
dev/ide_disk.hh:
    Major changes to fix bogus handling of dma transfers.  The read seems to
    work pretty well, but the write is unverfied until we can get a disk
    image that actually tries to write.
dev/tsunami_pchip.cc:
    Change mask to properly mask 13 bits not 12

--HG--
extra : convert_revision : 08fe9bc32970e449cd045de479553a96a4e389d6

dev/ide_disk.hh

@@ -313,6 +313,8 @@ class IdeDisk : public SimObject
                        (cmdReg.cyl_low << 8) | (cmdReg.sec_num));
     }
 
+    inline Addr pciToDma(Addr &pciAddr);
+
     /**
      * Serialize this object to the given output stream.
      * @param os The stream to serialize to.