Move fixup_partial_die to partial_die_info::fixup

Move fixup_partial_die to partial_die_info::fixup

fixup_partial_die can be a partial_die_info method fixup.

gdb:

2018-02-26  Yao Qi  <yao.qi@linaro.org>

	* dwarf2read.c (struct partial_die_info) <fixup>: New method.
	(fixup_partial_die): Remove declaration.
	(scan_partial_symbols): Update.
	(partial_die_parent_scope): Likewise.
	(partial_die_full_name): Likewise.
	(fixup_partial_die): Change it to partial_die_info::fixup.