aarch64: Improve atomic-op lse generation

Fix constraints; avoid unnecessary split.  Drop the use of the atomic_op
iterator in favor of the ATOMIC_LDOP iterator; this is simplier and more
logical for ldclr aka bic.

	* config/aarch64/aarch64.c (aarch64_emit_bic): Remove.
	(aarch64_atomic_ldop_supported_p): Remove.
	(aarch64_gen_atomic_ldop): Remove.
	* config/aarch64/atomic.md (atomic_<atomic_optab><ALLI>):
	Fully expand LSE operations here.
	(atomic_fetch_<atomic_optab><ALLI>): Likewise.
	(atomic_<atomic_optab>_fetch<ALLI>): Likewise.
	(aarch64_atomic_<ATOMIC_LDOP><ALLI>_lse): Drop atomic_op iterator
	and use ATOMIC_LDOP instead; use register_operand for the input;
	drop the split and emit insns directly.
	(aarch64_atomic_fetch_<ATOMIC_LDOP><ALLI>_lse): Likewise.
	(aarch64_atomic_<atomic_op>_fetch<ALLI>_lse): Remove.
	(@aarch64_atomic_load<ATOMIC_LDOP><ALLI>): Remove.

From-SVN: r265660