Fixes for functional accesses to use the snoop path.

Fixes for functional accesses to use the snoop path.
And small other tweaks to snooping coherence.

src/mem/cache/base_cache.hh:
    Make timing response at the time of send.
src/mem/cache/cache.hh:
src/mem/cache/cache_impl.hh:
    Update probe interface to be bi-directional for functional accesses
src/mem/packet.hh:
    Add the function to create an atomic response to a given request

--HG--
extra : convert_revision : 04075a117cf30a7df16e6d3ce485543cc77d4ca6