Add dwarf2_per_objfile parameter to get_die_type_at_offset

Add dwarf2_per_objfile parameter to get_die_type_at_offset

This allows removing some dwarf2_per_cu_data::dwarf2_per_objfile
references.

gdb/ChangeLog:

	* dwarf2/read.h (dwarf2_get_die_type): Add dwarf2_per_objfile
	parameter.
	* dwarf2/read.c (get_die_type_at_offset): Likewise.
	(read_namespace_alias): Update.
	(lookup_die_type): Update.
	(dwarf2_get_die_type): Add dwarf2_per_objfile parameter.
	* dwarf2/loc.c (class dwarf_evaluate_loc_desc) <get_base_type>:
	Update.
	(disassemble_dwarf_expression): Update.

Change-Id: Ibaf5b684cb0a8eb8f0b23e62bd0283c295410aa5