Move LiveProcess::create() from arch-specific files

Move LiveProcess::create() from arch-specific files
bcak to main LiveProcess, then automatically select
ISA based on object file type.  Now simulation scripts
no longer need to care about the ISA, as they can just
call LiveProcess().

configs/test/test.py:
    Script no longer cares about ISA.
src/arch/alpha/process.cc:
src/arch/alpha/process.hh:
src/arch/mips/process.cc:
src/arch/mips/process.hh:
src/arch/sparc/process.cc:
src/arch/sparc/process.hh:
src/sim/process.cc:
src/sim/process.hh:
    Move create() from arch-specific files back to
    main LiveProcess, then automatically select ISA
    based on object file type.

--HG--
extra : convert_revision : ef33ffdc79623b77000f5d68edd2026760b76ab6