Change objfile_has_partial_symbols to a method

Change objfile_has_partial_symbols to a method

This changes objfile_has_partial_symbols to be a method on objfile.

There are some other functions that could benefit from this sort of
change, but this was the only one that was relevant to this series.

gdb/ChangeLog
2021-03-20  Tom Tromey  <tom@tromey.com>

	* symfile.c (read_symbols): Update.
	* objfiles.h (struct objfile) <has_partial_symbols>: New method.
	(objfile_has_partial_symbols): Don't declare.
	* objfiles.c (objfile::has_partial_symbols): Rename from
	objfile_has_partial_symbols.
	(objfile_has_symbols, have_partial_symbols): Update.
	* elfread.c (elf_symfile_read): Update.
	* dwarf2/read.c (dwarf2_has_info): Update.
	* coffread.c (coff_symfile_read): Update.