PR29462, internal error in relocate, at powerpc.cc:10796

PR29462, internal error in relocate, at powerpc.cc:10796

Prior to the inline plt call support (commit 08be322439), the only
local syms with plt entries were local ifunc symbols.  There shouldn't
be stubs for other local symbols so don't look for them.  The patch
also fixes minor bugs in get_reference_flags; Many relocs are valid
only for ppc64 and a couple only for ppc32.

	PR 29462
	* powerpc.cc (Target_powerpc::Relocate::relocate): Rename
	use_plt_offset to pltcal_to_direct, invert logic.  For relocs
	not used with inline plt sequences against local symbols, only
	look for stubs when the symbol is an ifunc.
	(Target_powerpc::Scan::get_reference_flags): Correct reloc
	handling for relocs not valid for both 32-bit and 64-bit.