[IA64] Cleanup HPSIM code (was: Re: Enable early console for Ski simulator)

After my last patch we have a new header file for HP simulator use.
Here's code to use it for stuff that used to have `extern' statements
inline in the code.  Functionality should not change with this patch.

Signed-off-by: Peter Chubb <peterc@gelato.unsw.edu.au>
Signed-off-by: Tony Luck <tony.luck@intel.com>