Code cleanup: Split create_debug_types_hash_table

Code cleanup: Split create_debug_types_hash_table

DWARF-5 moved .debug_types into .debug_info and so the types reading code needs
to be reused more (in a future patch).

gdb/ChangeLog
2017-02-20  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* dwarf2read.c (create_debug_type_hash_table): New function from
	create_debug_types_hash_table.
	(create_debug_types_hash_table): Call create_debug_type_hash_table.
	(create_all_type_units, open_and_init_dwo_file): Update
	create_debug_types_hash_table callers.