Remove special handling for PC == 0.  With this, kgdb can now properly unwind across a page fault due to a null function pointer.  It does a better job than ddb now in fact.
Remove special handling for PC == 0.  With this, kgdb can now properly
unwind across a page fault due to a null function pointer.  It does a
better job than ddb now in fact.

Reviewed by:	marcel
MFC after:	3 days

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase