ppc476 plt call stubs

Fuss over bctr in call stubs.

	* elf32-ppc.c (BA): Define
	(ppc_elf_link_hash_table_create): Correct default_params.
	(write_glink_stub): Pad small plt call stub with "ba 0" rather
	than "nop" for ppc476_workaround.
	(ppc_elf_finish_dynamic_sections): Likewise for branch table
	and __glink_PLTresolve.  Ensure plt call stub at end of page
	doesn't allow fall-thru prefetch.