S12Z: Emit RELOC_S12Z_OPR instead of RELOC_EXT24 where appropriate.

S12Z: Emit RELOC_S12Z_OPR instead of RELOC_EXT24 where appropriate.

When assembling instructions which involve OPR references, emit
RELOC_S12Z_OPR instead of RELOC_EXT24.

bfd/
	* bfd-in2.h [BFD_RELOC_S12Z_OPR]: New reloc.
	* libbfd.h: regen.
	* elf32-s12z.c (eld_s12z_howto_table): R_S12Z_OPR takes non zero
	source field.  (md_apply_fix): Apply final fix
	to BFD_RELOC_S12Z_OPR.
	* reloc.c[BFD_RELOC_S12Z_OPR]: New reloc.

gas/
	* config/tc-s12z.c (emit_opr): Emit BFD_RELOC_S12Z_OPR instead of
	BFD_RELOC_24.
	* testsuite/gas/s12z/opr-indirect-expr.d: Expect R_S12Z_OPR instead
	of R_S12Z_EXT24.