scripts: Improve gen_kobject_list.py variable address determination

The gen_kobject_list.py script looks at DWARF debug information in the
elf file to determine the address of variables. Make sure that when
looking at DW_FORM_exprloc, it looks at both DW_OP_addr and
DW_OP_plus_uconst.

Signed-off-by: Nick Goote <ngoote@gmail.com>