Fix Altix 350 support (SHub1/PIC), broken when Altix 450 (SHub2/TIOCP)
support was added: prefetch cannot be set when consistent/coherent I/O
is wanted. It's one or the other or none.
Fix the L1 console, broken for the Altix 450. Using POLL and GETC
apparently does return any characters. Special SAL calls exists
for when the console is asynchronous. Replace the poll call with
getting the interrupt status and replace the getc call with an
interrupt read.

It is not known if this change breaks the Altix 350, but it is
assumed that it will not harm. testing will tell us...