Significant changes to ISA description to completely factor

Significant changes to ISA description to completely factor
out CPU model.  ISA description now generates multiple
output source files to (in theory) reduce compilation time.

arch/alpha/isa_desc:
    Update for parser changes.  Move most constructors
    out of class declarations (which are now in decoder.hh)
    and into decoder.cc.  Move all execute() methods into
    exec output.
arch/isa_parser.py:
    Significant changes to make ISA description completely
    independent of CPU model, and isolate model-dependent parts
    of parser into one little class (CpuModel).  Also split up code
    output into multiple files (a header, a main source file, and
    per-cpu execute() method files).

    Noticeable changes to language as a result.  See updated Doxygen
    documentation.
cpu/simple_cpu/simple_cpu.hh:
    SimpleCPUExecContext typedef no longer needed.
    Add forward declaration of Process.
cpu/static_inst.hh:
    SimpleCPUExecContext and FullCPUExecContext typedefs no longer needed.
    Make eaCompInst() and memAccInst() return const refs.

--HG--
extra : convert_revision : 71471f267804fafd0a881bac7445677e76334daf