gdb: allocate so_list with new, deallocate with delete

gdb: allocate so_list with new, deallocate with delete

Initialize all fields in the class declaration, change allocations to
use "new", change deallocations to use "delete".  This is needed by a
subsequent patches that use C++ stuff in so_list.

Change-Id: I4b140d9f1ec9ff809554a056f76e3eb2b9e23222
Approved-By: Pedro Alves <pedro@palves.net>
Reviewed-By: Reviewed-By: Lancelot Six <lancelot.six@amd.com>