sync.md: Add soft atomics ABI description.

sync.md: Add soft atomics ABI description.

	* config/sh/sync.md: Add soft atomics ABI description.
	(fetchop_name): Use 'or' instead of 'ior'.
	(fetchop_insn): Remove.
	(atomic_compare_and_swap<mode>_soft):
        Don't insert aligning nop after the write-back instruction.  Fix
	multi-line asm output formatting style.
        (atomic_fetch_<fetchop_name><mode>_soft): Likewise.
        (atomic_fetch_nand<mode>_soft): Likewise.
        (atomic_<fetchop_name>_fetch<mode>_soft): Likewise.
        (atomic_nand_fetch<mode>_soft): Likewise.

From-SVN: r182686