Set EN_MAS7_UPDATE HID0 bit for e500 core.

Without enabling this bit, tlbre and tlbsx don't update the MAS7 register,
resulting in garbage in the register after a read (rather, the previous setting
of it for a tlbwe). This can result in mmu_booke_mapdev_attr() thinking
mappings that should match actually don't, because tlb1_read_entry() can't
determine the correct address of a given entry.

MFC after: 11-RELEASE