Pass the location of the m5 console backdoor to the console

Pass the location of the m5 console backdoor to the console
instead of compiling it into the console version

dev/alpha_access.h:
    move serialization stuff to alpha_console.hh
    define the ALPHA_ACCESS_BASE in m5 instead of in console.c and
    have m5 pass the value to the console
dev/alpha_console.cc:
dev/alpha_console.hh:
    Move serialization stuff into a derived class of AlphaAccess
sim/system.cc:
    pass the value of ALPHA_ACCESS_BASE to the console code via
    the m5AlphaAccess console variable.

--HG--
extra : convert_revision : 0ea4ba239f03d6dad51a6efae0385aa543064117