Add support for CPU models to execute the effective

Add support for CPU models to execute the effective
address calculation and memory access portions separately.
Not currently used by any CPU models, but Kevin says he needs this.

Also clean up handling of execution tracing for memory accesses
(move it all into isa_desc and out of CPU models).

Got rid of some ancient unused code too.

arch/alpha/isa_desc:
    Add execute() methods to EAComp and MemAcc portions of memory
    access instructions, to allow CPU models to execute the effective
    address calculation and memory access portions separately.

    Requires the execution context to remember the effective address
    across the two invocations.  Added setEA() and getEA() methods to
    execution context to support this.  A model that does not use the
    split execution model can panic if these methods are called.

    Also added hook to call traceData->setAddr() after EA computation
    on any load or store operation.
arch/isa_parser.py:
    Call traceData->setData() on memory writes (stores).
cpu/simple_cpu/simple_cpu.cc:
    Get rid of unused code.
cpu/simple_cpu/simple_cpu.hh:
    Add (non-functional) setEA() and getEA() methods for new
    split memory access execution support.

--HG--
extra : convert_revision : bc2d2c758c4ca753812b9fa81f21038e55929ff0