Streamline interface to Request object.

Streamline interface to Request object.

src/SConscript:
    mem/request.cc no longer needed (all functions inline).
src/cpu/simple/atomic.cc:
src/cpu/simple/base.cc:
src/cpu/simple/timing.cc:
src/dev/io_device.cc:
src/mem/port.cc:
    Modified Request object interface.
src/mem/packet.hh:
    Modified Request object interface.
    Address & size are always set together now, so track
    with single flag.
src/mem/request.hh:
    Streamline interface to support a handful of calls that set
    multiple fields reflecting common usage patterns.
    Reduce number of validFoo booleans by combining flags for fields
    which must be set together.

--HG--
extra : convert_revision : 3b499de90d6d5f12f0cc7a9a788663265677fe10