Eliminate a redundant declaration.
Eliminate a "cast discards qualifiers" warning when building with gcc.
Pull out the fdt mapping code into intr.c. The arm_intrng branch also
defines this function allowing the mapping method to change when we move
to it.
Fix the unwinder to get past functions with no stack but may cause an
exception. In this case no registers will be updated but the link register
will be copied to the program counter to be used to find the calling
function. In this case the program counter may be updated and we should
continue with the trace.