Free sframe encoder context

Free sframe encoder context

Like the patch to free sframe decoder data, this also needs to ensure
the function doing the free is passed the actual context address.

bfd/
	* elf-sframe.c (_bfd_elf_write_section_sframe): Don't pass
	address of local var to sframe_encoder_free, pass the actual
	context address.
	* elf64-s390.c (elf_s390_link_hash_table_free): New function.
	(elf_s390_link_hash_table_create): Set hash_table_free.  Tidy
	zmalloc call.
	(_bfd_s390_elf_write_sframe_plt): Don't pass address of local
	var to sframe_encoder_free, pass the actual context address.
	* elflink.c: Include sframe-api.h.
	(_bfd_elf_link_hash_table_free): Free sframe encoder data.
	* elfxx-x86.c (elf_x86_link_hash_table_free): Likewise.
	(_bfd_x86_elf_write_sframe_plt): Don't pass address of local
	var to sframe_encoder_free, pass the actual context address.
libsframe/
	* sframe.c (sframe_encode): Free context on error return path.