scripts: gen_kobject_list: linker section for _thread_idx_map

In some circumstances, _thread_idx_map[] is all zero and the linker
decides to put it into BSS instead of DATA section. This results in
kernel objects being pushed away so the hash table is no longer
valid. This forces _thread_idx_map to be in the data section inside
the intermediate object file so it will be placed in the data
section in final binary.

Fixes #43618

Signed-off-by: Daniel Leung <daniel.leung@intel.com>