Fix commit 980aa3e6

Fix commit 980aa3e6

Commit 980aa3e6 was supposed to cure dyn_reloc counting problems, but
did the opposite.  For PIC we count two types of dyn_reloc, those on
pc-relative relocs, and the total.  If a sym needs pc-relative dyn
relocs then all the relocs are dynamic.  If not, then only those that
are must_be_dyn_reloc are dynamic.

	PR 20519
	* elf64-ppc.c (pc_dynrelocs): New function.
	(ppc64_elf_relocate_section): Use it and must_be_dyn_reloc to
	handle pic dynamic relocs.