gdb: add program_space parameter to lookup_minimal_symbol

>From what I can see, lookup_minimal_symbol doesn't have any dependencies
on the global current state other than the single reference to
current_program_space.  Add a program_space parameter and make that
current_program_space reference bubble up one level.

Change-Id: I759415e2f9c74c9627a2fe05bd44eb4147eee6fe
Reviewed-by: Keith Seitz <keiths@redhat.com>
Approved-By: Andrew Burgess <aburgess@redhat.com>