gdb: add program_space parameter to lookup_minimal_symbol_text

Make the current program space reference bubble up one level.  Use a
program space from the context whenever that makes sense.

Change-Id: Id3b0bf4490178d71a9aecdbf404b9287c22b30f5
Reviewed-by: Keith Seitz <keiths@redhat.com>
Approved-By: Andrew Burgess <aburgess@redhat.com>