Removed dynamic cast to get interrupt frequency and replaced with a

Removed dynamic cast to get interrupt frequency and replaced with a
virtual function in alphaaccess.cc

dev/alpha_console.cc:
dev/alpha_console.hh:
dev/platform.hh:
dev/tsunami.cc:
dev/tsunami.hh:
dev/tsunami_io.hh:
    Removed dynamic cast to get interrupt frequency and replaced with a
    virtual function

--HG--
extra : convert_revision : 01f514a33d8f76c6527ab25a713d5c86f9fd646e